Bring a large pot of salted water to a boil. Add 2 pounds raw, large peeled and deveined shrimp. Boil until the shrimp are pink and just opaque, about 1 ½ minutes for fresh or 3 minutes for frozen. Drain in a colander and run under cold water for about 1 minute to cool. Arrange on a paper towel-lined baking sheet in a single layer and pat dry. Refrigerate while you prepare the dressing.

Stir 2 finely chopped medium celery stalks, ¼ cup mayonnaise, ¼ cup plain Greek yogurt, 2 tablespoons finely chopped fresh chives, 2 tablespoons finely chopped fresh dill, 2 tablespoons lemon juice, 2 teaspoons Dijon mustard, and ½ teaspoon kosher salt together in a large bowl.

Stir in the shrimp and 1 thinly sliced medium English cucumber. Taste and season with more kosher salt and freshly ground black pepper as needed.