Cut fish into 4 oz portions. Combine ketchup, Worcestershire sauce and brown sugar in saucepan. Bring to boil, reduce heat and cook over low heat 5 to 7 minutes. Coat fish with sauce. Grill over charcoal or broil 4 minutes on each side, or bake in preheated 350 degree oven 15 minutes or until fish flakes slightly. To assemble: On bottom half of each bun place two lettuce leaves, a tomato slice and fish. Add top of bun and serve.