Preheat the oven to 425°F. Heat the oil in a large oven-proof skillet over medium-high heat until hot. Add the onion cook for about 5 minutes or until tender. Transfer to a large bowl, and set aside.
Spoon ½ cup of the enchilada sauce into the bottom of the skillet. Set aside the remaining enchilada sauce.
Add the green chiles, chicken, remaining enchilada sauce, sour cream, salt, cumin, and chili powder to the onion, and stir well to combine.
Layer 4 tortillas in a single layer in the bottom of the skillet. (Tear some of the tortillas if necessary).
Spoon half of the chicken mixture over the tortillas and sprinkle with half of the cheese. Repeat the layers, ending with the remaining cheese.
Cover the skillet with aluminum foil. (Coat the underside of the aluminum foil with cooking spray to prevent the cheese from stick.)
Bake for 20 minutes or until bubbly. Uncover and increase the oven temperature to broil. Broil for 2 minutes or until the cheese is browned.
Remove the skillet from the oven sprinkle with cilantro before serving, if desired.