Spray 13x9-inch (3-quart) glass baking dish with nonstick cooking spray. Cook sausage in large skillet over medium-high heat until no longer pink, stirring frequently. Drain.
Place bread cubes in sprayed baking dish. Sprinkle evenly with cooked sausage, mushrooms and onions.
In large bowl, combine eggs, half-and-half, dry mustard and salt; beat lightly. Slowly pour egg mixture evenly over mixture in baking dish; press down lightly. Sprinkle with cheese. Cover tightly; refrigerate at least 8 hours or overnight.
Heat oven to 350°F. Uncover; bake 1 hour or until golden brown and knife inserted in center comes out clean. Let stand 10 minutes before serving.