1.Bring Two Quarts Of Water To A Boil. Add Shrimp And Turn Off Heat. Let Shrimp Sit In The Hot Water For 3-5 Minutes, Until Flesh Is Opaque Throughout. 2.Remove Cooked Shrimp From Water And Rinse With Cold Water To Chill Immediately. 3.Meanwhile, Whisk Chili Sauce, Lemon Juice, Horseradish, And Onion Together To Make The Cocktail Sauce. 4.Toss Chilled Shrimp With Chopped Celery. 5.Line Cocktail Cups With Salad Greens. 6.Spoon In Shrimp Mixture, Top With Sauce, And Serve Cold.