Preheat the oven to 375°F (190°C) and lightly grease a 9 x 13-inch baking dish.
In a bowl, mix the shredded chicken with 1/2 teaspoon of the cumin, the chili powder, and the salsa (if using) until evenly combined.
Place about an even portion of the chicken mixture down the center of each tortilla, roll tightly, and arrange seam-side down in the prepared baking dish.
Make the white sauce: in a large pot over medium heat, melt the butter. Stir in the flour and cook for about 1 minute, stirring constantly.
Slowly whisk in the chicken broth and cook, stirring frequently, until the sauce begins to thicken, about 6 minutes.
Stir in the remaining 1/2 teaspoon cumin, 1 cup of the shredded cheese, diced green chiles, sour cream, salt, and pepper until the cheese melts and the sauce is smooth.
Pour the white sauce evenly over the rolled enchiladas in the baking dish. Sprinkle the reserved 1/2 cup shredded cheese on top.
Bake until the cheese is melted and lightly golden, about 25 minutes. Remove from the oven and sprinkle with chopped cilantro before serving.
