Melt butter in large skillet. Saute onion and green pepper just until tender. While onion mixture is cooking, combine remaining ingredients in small bowl. Remove cooked onion and peppers from skillet and set aside. Add steaks and fry on both sides.
When steaks are cooked, top them with onions and peppers and then cheese mixture. Cover and cook until cheese is melted. Serve hot on fresh bread or roll.