1 In A Large Pot, Bring To A Boil 4 Quarts Of Water, Salted With 2 Tbsp Salt. Add The Shrimp And Cook For 1 Minute To 2 Minutes Max, Depending On Size Of Shrimp. (Over-Cooking The Shrimp Will Turn It Rubbery.) Remove Shrimp With A Slotted Spoon And Place Into A Bowl Of Ice Water To Stop The Cooking. 2 Drain The Shrimp. Cut Each Piece Of Shrimp In Half, Or Into Inch-Long Pieces. Place Shrimp In A Glass Or Ceramic Bowl. Mix In The Lime And Lemon Juice. Cover And Refrigerate For A Half Hour. 3 Mix In The Chopped Red Onion And Serrano Chile. Refrigerate An Additional Half Hour. 4 Right Before Serving, Add The Cilantro, Cucumber, And Avocado.