In a skillet, brown beef and onion; drain fat. Stir in taco seasoning and tomato sauce; set aside. In a large bowl, mix together soup, sour cream and chilies. Place one tortilla in the bottom of a 10-in. pie plate. Combine beef mixture with half of soup mixture; spoon over tortilla. Sprinkle with 1 cup cheese; top with second tortilla. Top with remaining soup mixture and sprinkle with remaining cheese. Bake at 350° for about 30 minutes or until heated through. Let stand a few minutes before serving.