Prepare the dressing by mixing mayonnaise, sour cream, lime zest and juice, dill, mustard, garlic, salt, and pepper in a medium bowl. Set aside or refrigerate.

Bring a pot of water to a boil, add shrimp, and cook for about 2 to 3 minutes until pink and opaque. Remove from heat.

Prepare an ice water bath in a large bowl. Transfer cooked shrimp into the ice bath for about three minutes, then drain and chop into bite-sized pieces.

Combine chopped shrimp with green onions and diced cucumber in a mixing bowl. Pour in the prepared dressing and stir gently until evenly coated.