Preheat oven to 375°F (190°C). Heat olive oil in a large skillet over medium heat. Add diced onion and cook for 4 minutes until soft and translucent. Add garlic and cook for 1 minute until fragrant.
Add shredded chicken, black beans, corn, and green chiles to the skillet. Pour in enchilada sauce. Add cumin, chili powder, smoked paprika, garlic powder, salt, and pepper. Stir well and simmer for 5 minutes until combined and slightly thickened.
Lightly grease a 9 x 13 baking dish. Arrange a single layer of corn tortilla halves across the bottom, slightly overlapping to cover the surface.
Spread half of the chicken mixture evenly over the tortillas. Sprinkle one-third of the cheese mixture on top. Repeat with another layer of tortillas, remaining filling, and another third of cheese.
Add the remaining cheese evenly on top. Cover loosely with foil and bake for 20 minutes. Remove foil and bake an additional 15 minutes until cheese is golden and bubbling.
Let the casserole rest for 5 minutes before slicing. Drizzle with sour cream or crema, then garnish with cilantro, jalapeño slices, and avocado before serving.
