Best Shredded Zucchini Casserole

If you ask me, a good casserole is one of life’s simple pleasures.

This shredded zucchini casserole is a comforting side dish that makes the most of summer’s bounty. Tender zucchini gets mixed with savory Parmesan and sharp cheddar, then baked until golden.

It’s loaded with garlic and onions sautéed until soft, plus a blend of herbs that give it real flavor. A crispy Panko topping with melted butter and fresh thyme helps the whole thing come together.

It’s a family-friendly dish that works just as well for weeknight dinners as it does for potlucks and gatherings.

What Kind of Zucchini Should I Use?

For this casserole, medium-sized zucchini work best because they have fewer seeds and less water content than the really large ones. You want zucchini that are about 6-8 inches long and feel firm when you give them a gentle squeeze at the store. If you end up with larger zucchini, no worries – just be extra diligent about squeezing out the moisture after you shred them, since bigger zucchini tend to be waterier. Whether you use green zucchini or yellow summer squash, both will work great in this recipe, so grab whatever looks freshest at your market.

Options for Substitutions

This casserole is pretty forgiving when it comes to swaps, so here are some options if you need them:

• Zucchini: You can use yellow squash instead of zucchini, or even do a mix of both. The texture and cooking time will be pretty much the same, so no adjustments needed.
• Heavy cream: If you don’t have heavy cream, half-and-half or whole milk will work. The casserole might be slightly less rich, but it’ll still taste great.
• Panko breadcrumbs: Regular breadcrumbs can replace panko, though you’ll lose some of that extra crunch. You could also use crushed crackers like Ritz for a buttery twist.
• Parmesan cheese: Grated Romano or Asiago cheese make good substitutes for Parmesan and will give you that same salty, nutty flavor.
• Cheddar cheese: Feel free to swap cheddar with Gruyere, mozzarella, or Monterey Jack. You could even use a Mexican cheese blend if that’s what you have on hand.
• Dried herbs: Fresh herbs work too – just use about three times the amount called for in the recipe. So if it calls for 1 teaspoon dried, use 1 tablespoon fresh.

Watch Out for These Mistakes While Baking

The biggest mistake you can make with this casserole is skipping the step where you salt and drain the zucchini – if you don’t squeeze out that excess moisture with paper towels or a clean kitchen towel, you’ll end up with a watery, mushy casserole instead of a nicely set dish. Another common error is not letting the casserole rest for the full 5 minutes after baking, which gives it time to firm up and makes slicing much cleaner. If you’re watching it under the broiler at the end, don’t walk away – that buttery panko topping can go from golden brown to burnt in seconds, so keep a close eye on it. For extra insurance against sogginess, you can even let the salted zucchini sit for 20-30 minutes instead of just 15, then give it a really good squeeze to get out every last bit of liquid.

What to Serve With Shredded Zucchini Casserole?

This zucchini casserole is pretty filling on its own, but it pairs beautifully with some grilled chicken or pork chops if you want to add protein to your meal. A simple arugula salad with lemon vinaigrette cuts through the richness of all that cheese and cream, keeping things balanced. I also love serving this alongside roasted cherry tomatoes or a caprese salad since the fresh tomatoes complement the Italian herbs in the casserole. If you’re feeding a crowd, garlic bread or dinner rolls are always a hit for soaking up any extra cheesy goodness from the dish.

Storage Instructions

Store: Keep any leftover zucchini casserole covered with foil or in an airtight container in the fridge for up to 4 days. It makes great leftovers for lunch or a quick dinner throughout the week.

Freeze: This casserole freezes really well! Let it cool completely, then wrap tightly in plastic wrap and foil, or portion it out into freezer-safe containers. It’ll keep for up to 3 months in the freezer.

Reheat: Warm up individual portions in the microwave for about 2-3 minutes, or reheat the whole casserole covered with foil in a 350°F oven for 20-25 minutes until heated through. If reheating from frozen, thaw it overnight in the fridge first for best results.

Estimated Nutrition

Estimated nutrition for the whole recipe (without optional ingredients):

• Calories: 1700-1850
• Protein: 80-90 g
• Fat: 110-120 g
• Carbohydrates: 110-120 g

Ingredients

For the casserole base:

• 9 cups zucchini (shredded and squeezed dry to prevent sogginess)
• 1 1/2 tsp salt
• 2 tsp olive oil (I use Bertolli extra virgin)
• 1 large yellow onion, finely diced
• 4 garlic cloves, minced
• 3 eggs (room temperature, about 70°F)
• 1/3 cup heavy cream
• 1 1/2 tsp Dijon mustard
• 1 1/2 cups Panko breadcrumbs
• 1 1/4 cups freshly grated Parmesan cheese
• 1/2 tsp dried oregano
• 1/2 tsp dried basil
• 1/2 tsp garlic salt
• 1/2 tsp dried parsley
• 1/4 tsp smoked paprika
• 1/2 tsp freshly cracked black pepper
• 1/4 tsp crushed red pepper flakes

For the topping:

• 1 1/2 cups sharp cheddar cheese, shredded
• 1/3 cup Panko breadcrumbs
• 1 1/2 tbsp unsalted butter (melted and cooled)
• 1 tsp fresh thyme leaves

Step 1: Prepare Zucchini and Aromatics

• 9 cups zucchini
• 1 1/2 tsp salt
• 2 tsp olive oil
• 1 large yellow onion, finely diced
• 4 garlic cloves, minced

Shred the zucchini and toss it with salt in a colander, then let it sit for 15 minutes—this draws out excess moisture that would otherwise make the casserole watery.

While the zucchini drains, heat the olive oil in a skillet over medium heat and sauté the diced onion for 5 minutes until softened and translucent.

Add the minced garlic and cook for 2 minutes more until fragrant.

Once the zucchini time is up, press it firmly with paper towels or a clean kitchen towel to remove as much moisture as possible.

Step 2: Build the Binding Mixture

• 3 eggs
• 1/3 cup heavy cream
• 1 1/2 tsp Dijon mustard

In a small bowl, whisk together the room-temperature eggs, heavy cream, and Dijon mustard until well combined.

This mixture will act as the binder that holds the casserole together.

I find that using room-temperature eggs helps them incorporate more smoothly and creates a more uniform texture throughout the dish.

Step 3: Combine All Ingredients and Prepare for Baking

• pressed zucchini and sautéed aromatics from Step 1
• egg binding mixture from Step 2
• 1 1/4 cups Panko breadcrumbs
• 1 1/4 cups freshly grated Parmesan cheese
• 1/2 tsp dried oregano
• 1/2 tsp dried basil
• 1/2 tsp garlic salt
• 1/2 tsp dried parsley
• 1/4 tsp smoked paprika
• 1/2 tsp freshly cracked black pepper
• 1/4 tsp crushed red pepper flakes

Preheat your oven to 375°F.

In a large bowl, combine the pressed zucchini from Step 1, the sautéed onions and garlic from Step 1, the egg mixture from Step 2, the 1 1/4 cups panko breadcrumbs, grated Parmesan cheese, dried oregano, dried basil, garlic salt, dried parsley, smoked paprika, black pepper, and crushed red pepper flakes.

Mix everything thoroughly until the ingredients are evenly distributed and the breadcrumbs are fully incorporated.

Step 4: Assemble and Bake the Casserole

• zucchini mixture from Step 3
• 1 1/2 cups sharp cheddar cheese, shredded

Transfer the zucchini mixture from Step 3 into a 9×13 inch baking dish (or similar size), spreading it evenly.

Top with the shredded sharp cheddar cheese, distributing it uniformly across the surface.

Cover the dish with foil and bake at 375°F for 35 minutes until the casserole is set and the cheese begins to melt.

Step 5: Add Crispy Breadcrumb Topping

• 1/3 cup Panko breadcrumbs
• 1 1/2 tbsp unsalted butter
• 1 tsp fresh thyme leaves

While the casserole bakes, mix the remaining 1/3 cup panko breadcrumbs with the melted and cooled butter and fresh thyme leaves in a small bowl until the breadcrumbs are evenly coated.

After the casserole has baked for 35 minutes, remove it from the oven, uncover it, and sprinkle the buttered breadcrumb mixture over the top.

Return the casserole to the oven, uncovered, and bake for another 15 minutes until the topping is golden brown and crispy.

Step 6: Finish and Rest

For an extra-golden finish, broil the casserole at 425°F for 1-2 minutes, watching carefully to prevent burning.

Remove from the oven and let the casserole stand for 5 minutes before serving—this allows the structure to set fully so it will cut into neat portions.

I like to let it rest the full time even though it’s tempting to dig in right away, as it really makes a difference in how cleanly it slices.