Prep the oven and pan: Preheat the oven to 375°F (190°C).
Lightly coat a 9x13-inch baking dish with cooking spray.
Sauté the veggies: Warm olive oil in a skillet over medium heat. Add onion and red bell pepper. Cook 5–6 minutes until softened.
Stir in corn, cumin, chili powder, smoked paprika, and a pinch of salt and pepper. Cook 1 more minute. Remove from heat.
Mix the filling: In a large bowl, combine shredded chicken, black beans, half of the sautéed veggie mixture, and 1/2 cup enchilada sauce.
Add 1/4 cup Greek yogurt if you want a creamier texture. Toss until evenly coated.
Layer the base: Spread 1/2 cup enchilada sauce on the bottom of the baking dish. Place a layer of corn tortillas over the sauce, tearing some to fit and cover the surface.
Add filling and cheese: Spoon half of the chicken mixture over the tortillas.
Sprinkle with 1/2 cup cheese. Add a thin drizzle (about 1/3 cup) of sauce.
Repeat layers: Add another layer of tortillas, then the remaining chicken mixture, 1/2 cup cheese, and another drizzle of sauce.
Top and finish: Add a final layer of tortillas. Pour the remaining sauce over the top and spread evenly.
Sprinkle the last 1/2 cup of cheese (plus the extra 1/4 cup if you like it extra melty). Scatter the remaining sautéed veggies on top for color and texture.
Bake: Cover with foil and bake for 15 minutes. Remove the foil and bake 10–12 more minutes, until the cheese is bubbling and lightly golden at the edges.
Rest and garnish: Let the casserole rest 8–10 minutes so it sets for clean slices.
Top with chopped cilantro, sliced jalapeños, and avocado. Serve with lime wedges and a dollop of Greek yogurt or light sour cream.