1. Preheat the oven to 350°F. Lightly grease a 9×13-inch casserole dish and set it aside.

2. Heat the olive oil in a medium skillet over medium heat. Add the diced onion, minced garlic, ground cumin, salt, and black pepper. Sauté for 3 to 4 minutes until the onion is softened and fragrant.

3. Add the cooked shredded chicken to the skillet and stir well to combine with the onion and spices. Cook for 2 to 3 minutes until the chicken is heated through.

4. Remove the skillet from the heat and stir in 1 cup of the shredded Monterey Jack cheese until evenly mixed. Set the filling aside.

5. In a medium saucepan over medium heat, melt the butter. Whisk in the flour and cook for about 1 minute, stirring constantly, until smooth and lightly bubbling.

6. Slowly pour in the chicken broth while whisking continuously to prevent lumps. Continue whisking until the sauce is smooth.

7. Bring the sauce to a gentle simmer and cook for about 5 minutes, stirring often, until it thickens.

8. Remove the saucepan from the heat. Stir in the sour cream and chopped green chiles until fully combined. Taste and season with additional salt and black pepper if needed.

9. Spread about 1/2 cup of the sour cream sauce over the bottom of the prepared casserole dish.

10. Divide the chicken filling into 8 equal portions. Spoon one portion into the center of each tortilla.

11. Roll each tortilla tightly and place it seam-side down in the casserole dish.

12. Pour the remaining sauce evenly over the enchiladas, covering them from end to end.

13. Sprinkle the remaining 1 cup of shredded Monterey Jack cheese evenly over the top.

14. Bake for 20 to 30 minutes, or until the cheese is melted and the sauce is bubbling around the edges.

15. Let the enchiladas rest for 5 minutes before serving. Garnish with fresh cilantro or sliced jalapeños if desired.