Prepare tomatoes. If desired, remove skins by scalding quickly. Cut a slice from stem ends of tomatoes then scoop out pulp. Chill thoroughly.
Drain pulp, chope, then combine with an equal amound of chopped celery, chopped cucumber, coarsely chopped shrimp (depending on size); sprinkle with salt and pepper. Moisten shrimp mixture with mayonnaise. Refill tomato shells and place on lettuce leaves to serve.