Mmmmmm. I first had this delicacy at JoJo's in North Little Rock, Arkansas.
It seems to be a dietary staple in Texas, home of the Dallas-based Frito Lay company. The company line is that it was invented by Daisy Doolin, the mother of the company's founder. Whatever.
Here's how you do it:
1) Pour a can of chili into a microwave-proof container (a plastic sports cup is good) put a paper towel over the top to keep it from splattering and heat if for, oh, two to three minutes in the microwave.
2) The traditional way to make it is to take a large bag of Fritos, open up one side with a knife and pour the chili onto the Fritos in the bag. Now, Forgive me for trampling on Lone Star State tradition, but a bowl is considerably less messy than the bag and none of the good stuff gets trapped in the recesses of the bag. Although--to be fair--using a bowl does entail extra dishwashing. So you decide, bag or bowl--dealer's choice.
3) Top with shredded cheese and chopped onions.
Some people make a casserole and bake it in the oven, but this reeks of fastidiousness.
You can vary the toppings to suit your taste: jalapenos, green onions, tomatoes, salsa or Texas Pete hot sauce. You can also use your own favorite homemade chili with or without beans.
For those who are concerned about the correct vintage to accompany a Frito Chili Pie meal, the proper wine to serve is beer, probably a Corona or Dos Equis.