Preheat oven to 350 f. arrange bread in a single layer on a jelly roll pan.. bake at 350f for 20 minutes or until toasted. Place bread cubes in a large bowl,
Melt margerine in a large nonstick skillet over medium high heat. add mushroom and onion to pan; saute 10 minutes or until liquid evaporates and vegetables are tender. add onion mixture to bread; toss well to combine.
Arrange half of the bread mixture in a 13 by 9 in baking dish coated with cooking spray. sprinkle with half of the cheese and half the bacon; top with remaining bread mixture, cheese, and bacon.
Combine milk and next 4 ingrediants,stirring with a wisk. pour milk mixture over bread mixture. cover and refrigerate 8 hours.
Remove strata from refrigerator; let stand at room temperature 15 minutes. bake strata covered at 350f for 30 minutes. Uncover and bake an additional 15 minutes or until set. let cool slightly before serving.