1. Preheat oven to 375°F (190°C). Grease a 9×13-inch baking dish.
2. In a bowl, mix shredded chicken with 1/2 cup enchilada sauce, diced onion, cumin, and chili powder.
3. Spread a thin layer of enchilada sauce on the bottom of the baking dish. Add a layer of tortillas, tearing them to fit.
4. Top with a layer of chicken mixture, a drizzle of sauce, and a sprinkle of cheese. Repeat layers until ingredients are used, finishing with a generous cheese layer.
5. Cover with foil and bake for 20 minutes. Remove foil and bake for an additional 10 minutes, or until cheese is bubbly and golden.
6. Garnish with fresh cilantro and serve with sour cream if desired.