I have been making this for years. I first got the original recipe from my Mother-in-law, but have adapted it to fit our taste buds. You can add more or less green chiles. I use 2 percent milk, evaporated milk or even half n half. You may also you any cheese, I prefer the mexican style cheeses or sharp cheddar. The cheese taste better if you shred it yourself.*Do not use flour tortillas, they will change the flavor and be gummy, you may leave out the tortillas and crush some sun chips on top if desired*. One can make this in advance and place in refrigerator until ready to bake.
Cook chicken breasts and cut up into small cubes and put into a medium size bowl. Salt and pepper lightly.
Preheat oven to 350. Spray casserole dish with cooking spray.
Cover bottom of dish with buttered tortilla quarters, buttered side down. (For less calories you may omit the tortillas)
Mix together diced onion and green chilies. Either saute in a small amount of butter until clear and onion is tender or for less calories use no butter and microwave until onion is tender. Add this to the chicken and toss.
Add mushroom soup and milk. Mix together.
Put half of the chicken mixture over tortillas, sprinkle with cheese, add another layer of tortillas, meat mixture and top with shredded cheese. Cover with foil.
Bake at 350 for 40 minutes. Let sit for 5 minutes before serving.