Preheat the oven to 350°F (175°C).
In a skillet over medium heat, add the diced onion and sauté until translucent, about 3-4 minutes.
In a mixing bowl, combine the shredded chicken, 1 cup of enchilada sauce, black beans, corn, cumin, garlic powder, salt, and pepper. Mix well.
Lay out the tortillas on a flat surface. Place equal portions of the chicken mixture down the center of each tortilla. Roll the tortillas tightly and place them seam side down in a greased baking dish.
Pour additional enchilada sauce over the top of the rolled tortillas, making sure they are well covered.
Sprinkle shredded cheese evenly over the sauce.
Cover the baking dish with aluminum foil and bake in the preheated oven for 20 minutes.
After 20 minutes, remove the foil and bake for an additional 5 minutes, or until the cheese is bubbly and lightly golden.
Remove from the oven and let cool for a few minutes. Garnish with fresh cilantro if desired.