Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the shredded chicken, 1/2 cup of green enchilada sauce, 1/2 cup of shredded cheese, sour cream, diced onion, cilantro, cumin, garlic powder, salt, and black pepper. Mix well until all ingredients are evenly combined.
Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds on each side to make them pliable.
Spread 1/4 cup of green enchilada sauce on the bottom of a 9x13-inch baking dish.
Take a tortilla, fill it with about 1/4 cup of the chicken mixture, and roll it up tightly. Place the rolled tortilla seam-side down in the baking dish. Repeat with the remaining tortillas and filling.
Once all the enchiladas are in the dish, pour the remaining green enchilada sauce over the top and sprinkle with the remaining cheese.
Cover the dish with aluminum foil and bake for 20 minutes. Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Let the enchiladas cool for a few minutes before serving. Garnish with additional cilantro if desired.