Preheat oven to 350 degrees.
Spray 1 1/2 to 2 quart casserole with Pam. In saucepan, combine both cans of chili and water; heat to boiling, stirring occasionally.
Place 1/2 of the corn chips in bottom of prepared casserole. Cover with half the chili mixture. Sprinkle with 1/2 cup onion and half the grated cheese. Repeat layers, ending with grated cheese. Bake for 25 minutes or until heated through. Serves 4 to 6.
TIP: After wedges of pie are cut, top each with a tablespoon of sour cream. An excellent main course on a cold day.
