Spray an 8x11x2 casserole dish with nonstick cooking spray. Layer cubed bread, then top with cooked sausage, then potato slices, then cheese. Mix the eggs, milk, mustard, salt, and pepper in a bowl. Pour over casserole, cover, and refrigerate over night. In the morning, preheat oven to 350F. Bake casserole, uncovered for 30 minutes or until it is set.