01 - Preheat oven to 350°F (175°C). Grease a 9x13-inch baking dish.
02 - Combine shredded chicken, 1 cup Monterey Jack cheese, 1/2 cup sour cream, sliced green onions, garlic powder, ground cumin, salt, and black pepper in a mixing bowl. Stir until mixture is evenly blended.
03 - Melt butter in a saucepan over medium heat. Stir in all-purpose flour and cook, whisking, for 1 to 2 minutes until mixture is bubbling but not browned.
04 - Slowly pour in chicken broth while whisking. Continue to cook, stirring frequently, until slightly thickened, about 3 minutes.
05 - Remove saucepan from heat and whisk in sour cream, diced green chilies, onion powder, and salt until smooth.
06 - Divide chicken filling evenly among the flour tortillas. Roll each tortilla tightly and arrange seam-side down in the prepared baking dish.
07 - Pour the white sauce evenly over the filled tortillas. Sprinkle the remaining 1 cup shredded Monterey Jack cheese over the top.
08 - Place the dish in the oven and bake uncovered for 25 to 30 minutes, until the cheese is bubbly and lightly golden.
09 - Let enchiladas cool briefly. Garnish with chopped cilantro and extra green onions before serving.