In a medium bowl, combine mayonnaise, sour cream, lime juice and zest, fresh dill, Dijon mustard, and minced garlic. Stir until smooth and well-blended, then cover and refrigerate.

Fill a medium saucepan with water and bring it to a boil. Add shrimp and cook for 2-3 minutes until pink and opaque. Stir occasionally.

Prepare an ice water bath. Transfer cooked shrimp to ice bath for 3 minutes, then drain and chop into bite-sized pieces.

In a large mixing bowl, add chopped shrimp, diced cucumber, and sliced green onions. Pour the chilled dressing over and toss gently to coat.

Transfer to a serving dish and serve chilled, or store in an airtight container in the refrigerator.