Preheat oven to 350°F.Spray the baking dish with nonstick cooking spray. In a large bowl, mix chicken, shredded cheese, chili powder, cumin, salt, and pepper. Set aside.
In a medium saucepan over medium heat, melt butter. Stir in garlic, cook until fragrant. Whisk in flour, let it cook and thicken (about 1 minute). Whisking the entire time. Slowly add the chicken broth and whisk until smooth. Reduce heat to low. Stir in the sour cream and green chilis. Layer the baking dish with two whole tortillas (or 1 whole and 2 halves on each side if it covers more surface). Sprinkle half of the chicken mixture evenly over the tortillas. Drizzle one cup of creamy sauce over the top. Repeat with tortillas, chicken mixture, and one cup of sauce. Finish with a layer of tortillas then pour the remaining sauce over top. Sprinkle with 2 cups of cheese.
Bake 20 minutes then switch to broil for approximately 2 minutes or until the cheese is bubbly and golden. Slice and add desired toppings. Serve. Store leftovers in an airtight container in the refrigerator for 4-5 days.