Preheat your oven to 350°F (175°C).
In a skillet, sauté diced onion and minced garlic until translucent.
Add the shredded chicken, green enchilada sauce, black beans, cumin, and chili powder. Stir to combine.
Spread a thin layer of the chicken mixture in the bottom of a greased baking dish.
Layer four tortillas on top, then spread a portion of sour cream, followed by more chicken mixture and a sprinkle of cheese.
Repeat layers until all ingredients are used, finishing with a layer of tortillas topped with cheese.
Cover with foil and bake for 25 minutes. Then, remove the foil and bake for an additional 15 minutes until the cheese is melted and bubbly.
Let it cool for a few minutes before garnishing with fresh cilantro and serving.