Preheat the oven to 350°F (175°C). Lightly grease a 9x13-inch baking dish.
Cut each small flour tortilla in half and set aside.
In a large bowl, combine the shredded chicken, sour cream, black beans, 1½ cups of the enchilada sauce, drained corn, garlic powder, cumin, chili powder, salt, and half of the chopped cilantro; mix until evenly combined.
Spread one third of the chicken mixture evenly across the bottom of the prepared baking dish.
Arrange one layer of the halved tortillas over the chicken mixture, overlapping as needed to cover the surface.
Sprinkle one third of the shredded cheese over the tortillas.
Repeat the layers two more times: one third of the chicken mixture, a tortilla layer, and one third of the cheese. For the final (third) tortilla layer, pour the remaining enchilada sauce over the top tortillas and then sprinkle the remaining cheese.
Bake uncovered for 22–25 minutes, or until the cheese is bubbly and the casserole is heated through.
Remove from the oven and let stand a few minutes, then sprinkle with the remaining chopped cilantro and serve. Optional: serve with extra sour cream or chopped tomatoes if desired.