Combine sour cream, cream of chicken soup, cream of mushroom soup, onion, green chiles together and blend it well. Grease a large baking dish or a 9x13-inch cake pan. Layer half of hte tortillas in the bottom of the pan, top with half of the shredded chicken, then half of the cheese and cover with half of the sour cream soup mixture. Repeat the layers the same way, only save enough cheese to lightly top the casserole. Bake at 350 degrees for 40-50 minutes or until everything is toasted hot and bubbling. Hint: If you can get a can of Stokes brand Green Chile and Pork or Green Chile and Chicken Sauce, use it and substitute it for the cream of mushroom soup for the perfect taste!