Bring 6 cups water to a boil, and add shrimp; cook 3 to 5 minutes or just until shrimp turn pink. Drain and rinse in cold water.
Peel shrimp; devein, if desired. Chop.
Stir together mayonnaise and next 7 ingredients in a large bowl; add shrimp. Cover and chill until ready to serve.
Brush cornbread evenly with melted butter; place on a baking sheet.
Broil 5 inches from heat 3 minutes or until toasted.
Layer each cornbread slice with lettuce and tomato, and top with shrimp mixture.
*Medium-size frozen cooked shrimp, thawed, may be substituted.
**Light mayonnaise may be substituted for regular mayonnaise.