In a large skillet, saute the onion and peppers in butter until crisp-tender. Remove from the heat. Stir in spinach and cereal. Spoon into a greased 11-in. x 7-in. baking dish. Sprinkle with cheese.
In a large bowl, combine the eggs, milk, bacon, mustard, salt and pepper. Pour over cheese. Bake at 325° for 45-50 minutes or until knife inserted near the center comes out clean. Let stand for 10 minutes before cutting. Yield: 6-8 servings.