Combine the water and the seasoning packet in a large pot and bring to a boil.
Add shrimp and stir occasionally. Cook for 2-3 mins. or until shrimp just turn pink.
Drain and set shrimp aside to cool.
While shrimp cools, stir together the mayonnaise, onion, celery, lemon juice, salt and pepper.
When shrimp is cool, peel and devein it.
Coarsely chop the shrimp and then add it to the mayonnaise mixture.
Refrigerate for 2 hours or even overnight.
When ready to serve, spread butter on each side of open bread rolls and toast on 350 degrees (F) for about 10 mins.
Add a lettuce leaf to the open bread and then evenly layer on shrimp mixture. Top with avocado.
Serve and enjoy!
