Step 1: Sauté the Aromatics and Brown the Chicken
Preheat your oven to 375°F (190°C). In a large skillet or Dutch oven, heat 2 tablespoons of oil over medium-high heat. Add the diced onion and red bell pepper. Cook for 5-6 minutes until softened. Push vegetables to the side, add the remaining oil, and add the chicken pieces in a single layer. Season with taco seasoning, cumin, smoked paprika, salt, and pepper. Sear without moving for 3-4 minutes to get good color, then stir and cook until chicken is mostly cooked through, about 5 more minutes.

Step 2: Create the Saucy Simmer
Add the minced garlic to the skillet and cook for 1 minute until fragrant. Pour in the undrained can of Rotel tomatoes and green chilies and the chicken broth. Stir well, scraping up any browned bits from the bottom of the pan. Bring to a simmer, then reduce heat to medium-low, cover, and let it cook for 8-10 minutes. This allows the chicken to become fork-tender and absorb the flavors.

Step 3: Shred the Chicken & Make the Creamy Mixture
Remove the skillet from heat. Using two forks, shred the chicken directly in the skillet into bite-sized pieces—it should pull apart easily. In a separate large bowl, whisk together the condensed cream of chicken soup, sour cream, and the can of diced green chiles until smooth.

Step 4: Assemble the Casserole Layers
Grease a 9×13-inch baking dish. Spread half of the tortilla chips in an even layer on the bottom, breaking some to fill gaps. In a large bowl, combine the shredded chicken mixture (and all its juices), the black beans, and the corn. Stir to combine. Spoon half of this chicken-bean mixture evenly over the chips. Dollop half of the sour cream sauce mixture over that, then sprinkle with 1.5 cups of the Mexican cheese blend and 1 cup of the shredded cheddar.

Step 5: Repeat the Layers
Repeat the layers: remaining tortilla chips, remaining chicken-bean mixture, remaining sour cream sauce. Reserve the remaining cheeses for the top.

Step 6: Add the Final Cheese Blanket and Bake
Sprinkle the remaining 1.5 cups of Mexican blend and 1 cup of cheddar cheese evenly over the entire casserole, covering it completely. Cover the dish tightly with aluminum foil.

Step 7: Bake, Then Brown
Bake, covered, for 25 minutes. Then, carefully remove the foil and bake for an additional 15-20 minutes, or until the casserole is bubbling vigorously around the edges and the cheese on top is fully melted and starting to develop golden spots. Let it rest for 10 minutes before serving—this is crucial for it to set for clean scooping.