Prepare muffin mix as directed on package, adding half cup of the cheese with the mix. Set aside. (Do not bake.) Cook and stir chicken, soup, chilies, scallions, garlic and chili powder in a large saucepan until heated through. Spoon muffin mixture into a greased 2 litre casserole. Spoon hot soup mixture over muffin mixture to within 1 cm of the edge. Bake at 180ºC or 25 minutes or until cornbread is golden. Top with cheese.