1. Cook bacon in a large nonstick skillet over medium heat until crisp. Remove bacon from pan; crumble, and set aside. Add onion to drippings in pan; sauté 4 minutes. Add garlic, and sauté 1 minute. Remove from heat.
2. Combine milk and next 6 ingredients in a large bowl; stir well with a whisk. Add bread cubes to milk mixture, tossing to coat bread cubes.
3. Arrange half of bread cubes in bottom of an 11 x 7-inch baking dish coated with cooking spray. Top with 2/3 cup cheese and half of onion mixture. Add remaining bread cubes, 2/3 cup cheese, and remaining onion mixture. Top with tomato slices and crumbled bacon. Cover and chill at least 8 hours.
4. Preheat oven to 325°.
5. Bake, uncovered, at 325° for 55 minutes. Sprinkle with remaining cheese; bake an additional 5 minutes or until cheese melts. Let stand 5 minutes before serving.
carbo rating: 35