Preheat oven to 350 degrees. Place a layer of crushed corn chips in the bottom of a 13 x 9 baking dish (just enough to cover the bottom of the dish). Layer half of the chopped onions over the chips. Mix the three soups together in a large mixing bowl and poor half of it over the onion. Next, layer 1 can of the chicken and half of the shredded cheese over the soups. Repeat the above steps, using the remaining ingredients. Crumble a few corn chips on top. Bake at 350 for 45 minutes. Serve with salsa, guacamole, and sour cream, if desired.