1Heat oven to 350°F. In large bowl, mix chicken, vegetables, milk, onion, soup and mushrooms. Spread in ungreased 8-inch square (2-quart) glass baking dish.
2In medium bowl, mix cereal and melted butter, stirring until evenly coated. Stir in cheese. Spoon evenly over chicken mixture.
3Bake uncovered 35 minutes.