1Heat oven to 375°F. Spray 13x9-inch (3-quart) glass baking dish with cooking spray. In medium bowl, mix refried beans, tomato sauce and fajita seasoning mix. Stir in chicken.
2Spread 1/2 cup of the bean mixture over bottom of baking dish. Arrange 4 tortillas, overlapping if necessary, in baking dish. Top with half of remaining bean mixture, half of the stir-fry vegetables and 1 cup of the cheese. Repeat layers with remaining tortillas, bean mixture, stir-fry vegetables and cheese.
3Cover baking dish with foil. Bake 30 minutes. Uncover; bake 15 to 20 minutes longer or until hot and bubbly. Let stand 5 minutes before cutting.