Poach the shrimp by filling a medium saucepan with water and bringing it to a gentle simmer. Add a sprinkle of salt and any optional aromatics like lemon slices. Cook the shrimp for 2–3 minutes until they turn pink, then swiftly transfer them to an ice bath to stop the cooking process.

In a mixing bowl, combine mayonnaise, lemon juice, Dijon mustard, dill, salt, and pepper. Whisk until smooth. Taste and adjust the seasoning.

Gently fold in the cooled and dried shrimp, chopped celery, and red onion to the creamy dressing. Toss carefully until everything is evenly coated.

Cover the bowl with plastic wrap and refrigerate the salad for at least 30 minutes.