Preheat your oven to 350 degrees. Spray a 9 by 13 inch baking dish with cooking spray and set aside.
In a large skillet for the enchilada sauce, heat 1 tablespoon oil over medium heat. Add 1 diced onion and 1/2 teaspoon kosher salt. Saute until the onion is translucent, about 5 minutes.
While the onion is cooking for the enchilada sauce, make the enchilada filling. In a bowl mix together the shredded chicken, salt, black pepper, diced green chiles, and drained black beans.
Stir chili powder and cumin into the onion for the enchilada sauce and cook for about thirty seconds. Then stir in 1 tablespoon all purpose flour. Slowly whisk in chicken stock. Then stir in the tomato sauce and minced garlic. Bring to a simmer and cook, stirring occasionally for 5 minutes.
Transfer the enchilada sauce to a blender and blend to make smooth (optional). Pour 1/2 cup in the bottom of the prepared baking dish. Pour 1/2 cup of enchilada sauce into the chicken mixture.
Dip 6 tortillas in the remaining sauce to coat them and line the bottom of the casserole dish with them.
Divide the chicken mixture in half, and add half of it to the top the tortillas in the pan. Top with 1 cup of cheese.
Dip the remaining 6 tortillas in the enchilada sauce and top with the remaining chicken mixture. Pour any remaining sauce over the casserole and top with 2 cups of colby jack cheese.
Bake uncovered for 25 minutes or until the cheese is bubbly.