Dice the celery stalks into 1/4-inch pieces, finely dice the green pepper, and chop the chives. Set aside the celery leaves for garnish. Measure out the mayonnaise, mustard, tarragon, mint, lemon zest, and black pepper into small bowls so everything is ready when you need it. This prep work ensures you won't be scrambling while the shrimp cooks.
Bring 4 cups of water to a boil in a large pot. Add the lemon slices (which add brightness and subtle flavor), salt, and 1 1/2 tsp seafood seasoning, then reduce heat to medium-low and maintain a gentle simmer. Add the frozen shrimp directly to the simmering water and cook for 2-3 minutes until they turn pink and opaque throughout. I find that cooking shrimp just until they turn color prevents them from becoming rubbery, so watch the clock carefully.
Using a slotted spoon, transfer the cooked shrimp to a bowl filled with ice water to stop the cooking process immediately. Let them cool for a couple of minutes, then drain well. Once cool enough to handle, chop the shrimp into bite-sized pieces—I prefer leaving them a bit chunky rather than mincing them too fine, as this gives the salad better texture and makes each bite more satisfying.
In a large mixing bowl, combine the chopped shrimp with the diced celery, green pepper, and chives prepared in Step 1. Add the remaining 1 1/4 tsp seafood seasoning, tarragon, and mint from your mise en place, and gently toss everything together to distribute the seasonings evenly. This step ensures the herbs and spices are incorporated throughout before the creamy dressing is added.
In a separate small bowl, whisk together the mayonnaise, mustard, lemon zest, and black pepper until smooth and well combined. Pour this dressing over the shrimp and vegetable mixture, then gently fold everything together until the salad is evenly coated and creamy. Taste the salad and adjust seasoning as needed—sometimes a pinch more salt brings out the flavors beautifully.
Transfer the creamy shrimp salad to a serving bowl or storage container and refrigerate for at least 1 hour before serving. This chilling time allows the flavors to meld and develop. Just before serving, give it a gentle stir and garnish with the reserved celery leaves for a fresh, herbaceous finish.