"This light, fluffy and flavorful casserole contains cheese, onions and mushrooms. It is easy to make and contains ingredients found in most kitchens. No or low fat ingredients and whole wheat bread make for a healthy alternative. This dish works equally well for a delicious family breakfast/brunch or for guests."
Spray a 9 X 13 inch baking dish with a no-stick cooking spray. Arrange the slices of bread in the baking dish.
Melt the margerine in a medium size frying pan and add the chopped onion, cooking over medium heat for five minutes or until the onions are soft.
Sprinkle the bread with the onions, mushrooms and cheese.
Mix the milk, eggs, mustard, salt and garlic powder together and pour the mixture over the bread. Lightly press the top of the bread slices to help soak up the liquid mixture. (Alternatively, the casserole may be refrigerated for several hours or overnight.)
Bake uncovered for 25 minutes, or until the top is a golden brown.