Place shrimp in a pot with lightly salted, boiling water. Cook for about 3 minutes or until pink and opaque. Do not overcook shrimp. Once cooled, remove shells from shrimp and cut into about 1/2 inch pieces
In a bowl mix together shrimp, onion, red pepper, cucumber, green onion, jalapeño, cilantro, juice from 1/4 lime, and mayo. Stir together and set aside
Cut avocados in half, remove pit and skin from avocados. Drizzle lime juice on top of avocados to keep from browning. Stuff avocados with shrimp salad and place on a bed of shredded lettuce. Add extra cilantro and lime juice on top to serve