1. Combine onion, green pepper, and butter in a 9-inch round baking dish. Microwave, uncovered, at Time Cook (power level 10) for 5 minutes, stirring twice.
2. Add remaining ingredients, except rolls, to baking dish. Microwave, uncovered, at Time Cook (power level 7) for 4 1/2 to 5 minutes, or until nearly firm, stirring and breaking up the mixture once after 2 1/2 minutes' cooking time. Let stand 2 to 3 minutes before serving to allow to set completely. Cut into wedges and place on rolls. If desired, spread with mayonnaise and top with lettuce.