Mince the onion.

Saute the minced onion in butter until softened.

Dice the cooked chicken.

Shred the cheddar cheese.

In a large bowl, combine the sauteed onion, diced chicken, 3 cups of shredded cheese, cream of mushroom soup, lowfat sour cream, and minced green chilies.

Mix all ingredients well.

Grease a 9x13 inch baking dish.

Place half of the corn tortillas in the prepared baking dish, overlapping as needed to cover the bottom.

Spread half of the chicken mixture evenly over the tortillas.

Repeat the layers with the remaining tortillas and chicken mixture.

Sprinkle the remaining 1 cup of shredded cheese over the top of the casserole.

Bake in a preheated oven at 350 degrees Fahrenheit (175 degrees Celsius) for 50 minutes, or until bubbly and golden brown.

Let cool slightly before serving.

Enjoy!