Begin by filling a large pot with water and bringing it to a gentle simmer over medium heat. Add a sprinkle of salt and flavor the water with lemon slices or a bay leaf if desired. Carefully add the shrimp and poach for 2-3 minutes until they turn pink and opaque.

Once the shrimp are done, quickly transfer them to an ice bath using a slotted spoon. Fill a large bowl with ice and cold water, then let the shrimp chill for 5-7 minutes. After chilling, drain the shrimp and pat them dry with paper towels.

In a medium mixing bowl, combine mayonnaise, fresh lemon juice, Dijon mustard, and chopped dill. Season with salt and pepper to taste, stirring until well blended.

Add the cooled shrimp, chopped celery, and minced red onion to the bowl with the dressing. Gently toss the mixture until all the ingredients are thoroughly coated with the dressing.

Cover the shrimp salad with plastic wrap and refrigerate for at least 30 minutes, allowing the flavors to meld together.