Cook shrimp in boiling, salted water 3 minutes or just until cooked. Cool, peel, and roughly chop shrimp.
Squeeze limes into a medium bowl. Add shrimp, shallot, and next 7 ingredients, stirring until well blended. Chill at least 1 hour and up to 6.
Stir cilantro and diced avocados into chilled shrimp mixture. Serve with a slotted spoon.