Preheat the oven to 375°F and lightly grease a 9x13 baking dish. Spread a thin layer of enchilada sauce across the bottom of the dish to prevent sticking during baking.

If making the optional homemade enchilada sauce, heat vegetable oil in a saucepan over medium heat and whisk in the flour. Cook for about 1 minute until smooth, then stir in the chili powder, cumin, garlic powder, onion powder, oregano, salt, and pepper. Slowly whisk in the chicken broth and tomato sauce and simmer for 10–12 minutes until slightly thickened.

Heat vegetable oil in a skillet over medium heat. Add the chopped onion and garlic and sauté until softened and fragrant, about 3–4 minutes.

Add the shredded chicken along with cumin, chili powder, salt, and pepper. Stir well so the seasoning evenly coats the chicken and continue cooking for another few minutes.

Warm the tortillas slightly so they roll easily without tearing. Spoon the chicken mixture into the center of each tortilla and top with shredded Monterey Jack cheese.

Roll each tortilla tightly and place seam-side down into the prepared baking dish. Continue until all the enchiladas are assembled.

Pour the enchilada sauce evenly over the tortillas and top with the remaining cheese for a fully melted, bubbly finish.

Bake uncovered for 20–25 minutes until the cheese is melted and bubbling around the edges. Allow the enchiladas to cool for several minutes before serving with sour cream, avocado, cilantro, or jalapeños if desired.