Prepare the slow cooker liner with nonstick cooking spray. In a large bowl, mix together the precooked diced chicken, half the enchilada sauce, cream cheese, green chiles, and sour cream until well blended.
Layer the casserole in the slow cooker by adding enough of the chicken mixture to cover the bottom. Then add a layer of tortillas, overlapping to cover the bottom contents, a small amount of enchilada sauce, and then a sprinkle of cheese.
Continue adding layers in this order ending with the remaining enchilada sauce and cheese. Cover and cook on low for 5 to 6 hours. Serve topped with sour cream, shredded cheese, and/or chopped cilantro..