Place toast on baking sheet. Spread with butter if desired. Cover with mushrooms and tomato slices. Sprinkle cheese and crumbled bacon on top. Bake in 350 degree oven until cheese melts. 1 serving 147 cal or 1 bread, 1 fat and 1 lean meat exchange (without butter) or 182 cal or 1 bread, 2 fat and 1 lean meat exchange (with butter).