01 - Preheat the oven to 350°F (175°C) and lightly grease a 9x13-inch baking dish.
02 - Combine shredded chicken, 1 cup Monterey Jack cheese, 1/2 cup sour cream, green onions, garlic powder, cumin, salt, and black pepper in a large bowl. Mix thoroughly.
03 - In a saucepan over medium heat, melt unsalted butter. Stir in all-purpose flour and cook, whisking constantly, for 1 to 2 minutes, ensuring the mixture bubbles but does not brown.
04 - Gradually add chicken broth, whisking continuously. Continue stirring until the sauce begins to thicken, approximately 3 minutes.
05 - Remove the pan from heat. Whisk in sour cream, diced green chilies, onion powder, and salt until the sauce is smooth.
06 - Evenly divide the chicken filling among the 8 tortillas. Roll up each tortilla and arrange seam-side down in the prepared baking dish.
07 - Pour the white sauce evenly over the rolled tortillas. Sprinkle with the remaining 1 cup Monterey Jack cheese.
08 - Bake uncovered for 25 to 30 minutes, until the sauce is bubbling and the cheese is lightly golden.
09 - Let the enchiladas cool briefly. Garnish with chopped cilantro and additional sliced green onions before serving.