In a medium bowl, combine mayonnaise, sour cream, lime zest and juice, dill, Dijon mustard, and minced garlic. Whisk until smooth and well-blended. Chill while preparing the salad.

Bring a medium pot of water to a boil. Add the shrimp and cook for 2-3 minutes until pink and opaque. Drain in a colander.

Prepare an ice water bath. Transfer the shrimp to the ice bath to cool for 3 minutes, then drain and pat dry.

In a large mixing bowl, combine the chilled shrimp, diced cucumber, and sliced green onions. Pour the dressing over and gently fold until well coated.

Transfer to a serving dish or bowls. Can be served immediately or refrigerated for later enjoyment. Garnish with additional dill or lime wedges if desired.