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, drained black beans, 1½ cups of the enchilada sauce, drained corn, ½ of the chopped cilantro, garlic powder, cumin, chili powder, and salt; stir until evenly mixed.
Spoon one third of the chicken mixture into the bottom of the prepared baking dish and spread into an even layer.
Arrange a single layer of the halved tortillas over the chicken mixture, then sprinkle one third of the shredded cheese on top.
Repeat layering: add one third of the chicken mixture, a layer of tortillas, and one third of the cheese.
For the final layer, add the remaining chicken mixture, top with the remaining tortillas, pour the remaining enchilada sauce over the top, and sprinkle with the remaining cheese.
Bake uncovered for 22–25 minutes, or until the cheese is bubbly and heated through.
Remove from the oven and let rest a few minutes, then garnish with remaining chopped cilantro and serve with extra sour cream or chopped tomatoes if desired.