1. Sauté mushrooms and onion in a nonstick skillet coated with cooking spray over medium-high heat 8 minutes or until onion is tender. Remove from skillet, and place in a large bowl.
2. Cook sausage in skillet 8 minutes or until sausage crumbles and is no longer pink; drain well on paper towels. Stir together sausage, eggs, and next 4 ingredients with mushroom mixture in bowl. Pour mixture into a 10-inch quiche dish or deep-dish pieplate coated with cooking spray.
3. Bake at 350° for 30 minutes or until set. Let stand 5 minutes before serving. Slice into 8 wedges.
* One (1-pt.) container of egg substitute may be substituted for the 4 whole eggs and 8 egg whites.