Begin by filling a medium saucepan with salted water and optional lemon slices. Heat over medium until it reaches a gentle simmer. Carefully add raw shrimp to the water and poach for 2-3 minutes. The shrimp should turn pink and opaque. Once cooked, use a slotted spoon to transfer them to an ice bath, halting the cooking process and preserving their tender texture.

In a mixing bowl, combine creamy mayonnaise, fresh lemon juice, Dijon mustard, dill, salt, and freshly cracked pepper. Whisk vigorously until the mixture is smooth and well-blended. Taste and adjust the seasoning for your preferences.

In a large mixing bowl, take your poached shrimp and add in diced celery and minced red onion. Carefully drizzle the prepared dressing over these ingredients. Gently toss everything together using a spatula, ensuring the shrimp and vegetables are evenly coated.

Cover the shrimp salad with plastic wrap or a tight-fitting lid, then place it in the refrigerator. Allow it to chill for at least 30 minutes.

Once chilled, give the shrimp salad another gentle stir and taste for final adjustments. Serve it in various ways: as a filling for a sandwich, on crisp crackers, or in lettuce cups.