Preheat your oven to 350°F and grease a 9x5 inch loaf pan (or similar bread pan) with cooking spray or butter, making sure to coat the bottom and all sides evenly. This prevents sticking and ensures easy removal once baked.

In a large mixing bowl, combine the oats, baking soda, salt, cocoa powder (sifted to remove lumps), and espresso powder. Whisk these together thoroughly to evenly distribute the leavening agent and cocoa throughout—this ensures the bread rises uniformly and has consistent chocolate flavor in every bite.

In a separate bowl or blender, combine the mashed banana, squeezed zucchini (it's critical to squeeze out excess moisture or your bread will be soggy), maple syrup, eggs, milk, and vanilla extract. Blend or whisk until smooth. Pour this wet mixture into the bowl with your dry ingredient mixture from Step 2, and stir until just combined—don't overmix, as this keeps the bread tender. I like to use a food processor to blend the wet ingredients first since it creates a smoother, more integrated batter that bakes more evenly.

Gently fold the bittersweet chocolate chips into the batter from Step 3 using a spatula or wooden spoon, distributing them evenly throughout. Pour the batter into your prepared pan from Step 1, smoothing the top with a spatula for even baking.

Place the pan in your preheated 350°F oven and bake for 35-40 minutes, until a toothpick inserted into the center comes out clean or with just a few moist crumbs (not wet batter). The bread should be set but still have a tender crumb structure.

Remove the bread from the oven and let it cool in the pan for 10-15 minutes before turning it out onto a wire rack. I prefer to let the bread cool completely in the pan first—this prevents it from breaking apart while still warm. Allow it to cool completely before slicing to get clean, neat slices and to allow the flavors to fully develop.