1. Generously butter a 9 x 13 baking dish.
2. Arrange the bread in the baking dish and sprinkle with cheese.
3. In a bowl, combine the eggs, milk, mustard, salt, cayenne and onion powder.
4. Pour this mixture over the bread.
5. Sprinkle with the bacon, mushrooms and tomatoes.
6. Cover and chill up to 24 hours.
7. Preheat oven to 325*F.
8. Bake uncovered for about one hour or until the mixture sets.
9. Tent with foil if the top begins to over brown.