Preheat the oven to 375°F (190°C) and lightly grease a 9 x 13-inch casserole pan.
In a mixing bowl, combine the shredded cooked chicken with 1/2 teaspoon of the cumin, the chili powder, and the salsa (if using); mix until evenly coated.
Place about an equal portion of the chicken mixture down the center of each tortilla, roll up, and arrange seam-side down in the prepared casserole pan.
Make the white sauce: in a large pot over medium heat, melt the butter. Whisk in the flour and cook for 1 minute, stirring constantly.
Slowly pour in the chicken broth while whisking, then cook and stir until the sauce begins to thicken, about 6 minutes.
Stir in the remaining 1/2 teaspoon cumin, 1 cup of the shredded cheese, the diced green chiles, sour cream, sea salt, and black pepper; cook until the cheese is melted and the sauce is smooth.
Pour the white sauce evenly over the arranged enchiladas, sprinkle the remaining 1/2 cup shredded cheese on top, and bake for 25 minutes or until the cheese is lightly golden.
Remove from the oven and sprinkle the chopped cilantro over the enchiladas before serving.