Preheat the oven to 375°F and lightly grease a 9x13 baking dish.
Heat a skillet over medium heat. Add the diced onion and cook until softened. Stir in the shredded chicken, cumin, salt, and pepper. Remove from heat.
Spread a thin layer of enchilada sauce in the bottom of the baking dish. Add half the tortilla strips, half the chicken mixture, half the black beans, and one cup of cheese. Repeat the layers once more, ending with the remaining cheese on top.
Pour the rest of the enchilada sauce evenly over the top. Bake for 25 minutes until the cheese is melted and the edges are bubbling.
Let the casserole rest for 5 minutes before serving.