Chili Frito Casserole

1 large package Fritos (about 4 to 5 cups)
2 large onions, peeled and chopped
1 pound American cheese, grated
4 cups leftover or canned chili

Place about a third of the Fritos in the bottom of a 2-quart casserole dish. Spread on half the chili, onions and cheese in layers. Repeat the layers, ending with Fritos. Bake at 350 degrees F for about half an hour until browned and bubbling in the center. Serve hot.