01 - Preheat oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
02 - In a large mixing bowl, combine shredded chicken, Monterey Jack cheese, sour cream, green onions, garlic powder, ground cumin, salt, and black pepper until well blended.
03 - In a medium saucepan, melt unsalted butter over medium heat. Stir in all-purpose flour and cook for 1 to 2 minutes until the roux is bubbling but not browned.
04 - Gradually whisk in chicken broth. Cook, stirring continuously, until slightly thickened, about 3 minutes.
05 - Remove saucepan from heat. Whisk in sour cream, diced green chilies, onion powder, and salt until the sauce is smooth and creamy.
06 - Divide the chicken mixture evenly among the flour tortillas. Roll each tortilla tightly and arrange seam-side down in the prepared baking dish.
07 - Pour the prepared white sauce evenly over the filled tortillas. Sprinkle the remaining Monterey Jack cheese over the top.
08 - Bake uncovered for 25 to 30 minutes, or until the dish is bubbling and the surface is lightly golden.
09 - Allow the enchiladas to cool briefly. Garnish with freshly chopped cilantro and additional green onions before serving.