In a small skillet, cook onion in oil until tender. Add garlic; cook 1 minute longer. Remove from the heat. In a large bowl, combine onion mixture, sour cream, half of the cheese, milk, chilies and cumin. Stir in hominy.
Pour into a greased 2-qt. baking dish. bake, uncovered, at 350° for 30 minutes or until heated through. Sprinkle with remaining cheese.