Bring a pot of salted water to a gentle boil. Add shrimp and cook just until they turn pink and opaque, about 1–2 minutes depending on size. Do not overcook.
Immediately transfer shrimp to an ice bath or rinse under cold running water to stop the cooking; drain well.
If desired, slice shrimp into bite-sized pieces for easier eating and a crisp cucumber-to-shrimp ratio.
Make the Dressing
In a medium bowl, whisk together mayonnaise, sour cream, lime zest, lime juice, Dijon mustard, minced garlic, chopped dill, and kosher salt. Taste and add black pepper as needed.
Combine and Chill
Add diced cucumber and sliced green onions to the dressing and toss to coat.
Gently fold in the cooled shrimp until everything is evenly coated.
Refrigerate for at least 30 minutes (up to 2 hours) to let flavors marry. Serve chilled.
Notes
Swap Greek yogurt for the sour cream to cut calories. Use regular cucumbers if you don’t have an English cucumber; peel and seed to reduce bitterness. If you can’t find dill, substitute with fresh parsley plus a pinch of lemon zest.