Melt the butter in a skillet over medium heat. Add the bell pepper, onion, and celery and saute for 2 minutes.
In a bowl, combine the soup, mayonnaise, Parmesan, crabmeat, shrimp, and pepper. Stir the sauteed vegetables into the seafood mixture and spoon this mixture into a lightly greased 8 x 11-inch casserole dish. Bake for 30 minutes. Serve with toast points or crackers.