Preheat your oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish with cooking spray or a bit of butter.
In a large bowl, mix the shredded chicken, green enchilada sauce, sour cream, green chiles, garlic powder, onion powder, salt, and pepper. Stir until everything is well combined and creamy.
Lay 4 tortillas on the bottom of the baking dish, tearing them if needed to cover the base. Spread half the chicken mixture on top, then sprinkle with 1 cup of shredded Monterey Jack cheese.
Add the remaining 4 tortillas, top with the rest of the chicken mixture, and sprinkle the remaining 1 cup of cheese over everything.
Bake uncovered for 25–30 minutes, until the cheese is melted, bubbly, and the edges start to brown slightly.
Let the casserole sit for a few minutes before serving. Garnish with chopped cilantro if you’d like, and add a little sour cream on the side for extra flavor.