Cut fish into serving size pieces. Cook onion, green pepper & garlic in butter until tender. Add remaining ingredients; simmer 5 minutes, stirring occasionally. Cool. Place steak pieces in single layer in shallow baking pan; pour sauce over fish & let stand for 30 minutes, turning once. Remove fish, reserving sauce for basting. When coals are ready, place fish in well greased, hinged wire grills. Cook on bbq grill 4" from heat for 8 minutes. Baste with remaining sauce, turn, & cook for 7-10 minutes longer.