In a large pot, combine 2 quarts of water, the halved lemon, smashed garlic cloves, bay leaf, salt, and optional Cajun seasoning. Bring to a boil over medium-high heat. Remove from heat, add shrimp, and let sit for 3 minutes until pink and opaque.

Finely dice the red bell pepper and celery, and thinly slice the green onion, keeping parts separate. Set aside in a large mixing bowl.

In the same bowl, add mayonnaise, fresh lemon juice, and chopped dill. Sprinkle in salt and pepper, and blend until creamy.

Once cooled, add shrimp to the bowl with dressing and vegetables. Gently fold until coated.

Cover and refrigerate for at least 1 hour to meld flavors.

Serve on leafy greens or with crackers, sandwiches, or lettuce wraps.