Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add sausage and next 3 ingredients; sauté 9 minutes or until sausage is browned and vegetables are tender. Drain and set aside.
Cut muffin halves into quarters, and arrange in an 11 x 7-inch baking dish coated with cooking spray. Sprinkle half of sausage mixture and 1 cup cheese over muffins.
Combine eggs, egg whites, and next 3 ingredients in a large bowl; stir well with a whisk. Pour evenly over mixture in baking dish. Top with remaining sausage mixture and remaining 1 cup cheese. Cover and chill at least 8 hours.
Preheat oven to 350°.
Bake, uncovered, at 350° for 45 minutes. Let stand 10 minutes before serving.