Prepare muffin mix as directed on package, adding 1/2 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 quart casserole. Spoon hot soup mixture over muffin mixture to within 1/2" of the edge. Bake at 350 degrees for 25 minutes or until cornbread is golden. Top with cheese.