Preheat your oven to 350°F (175°C) and lightly grease a medium-sized baking dish with cooking spray or butter.

Season the boneless, skinless chicken breasts generously with garlic salt and place them in the preheated oven. Bake for approximately 45 minutes or until the chicken reaches an internal temperature of 165°F (74°C).

While the chicken is cooling, char the tortilla halves on an open flame for about 1 minute until they puff up.

Pour about 1/2 inch of green chile enchilada sauce into the bottom of your greased baking dish and layer six of the charred tortilla halves on top.

Top with half of the shredded chicken, one-third of the Monterey Jack cheese, half of the sour cream, and one-third of the remaining enchilada sauce.

Repeat layering with another set of tortilla halves, remaining shredded chicken, cheese, sour cream, and the rest of the enchilada sauce.

Cover the casserole with aluminum foil and bake for 45 minutes, then remove the foil and bake for an additional 10 minutes.

Let the casserole cool slightly for about 10 minutes before serving.