Step 1: Preheat and Prepare the Filling Base
Preheat your oven to 400°F (200°C). Lightly grease a 9×13 inch (23x33cm) baking dish. In a large skillet or Dutch oven, heat the olive oil over medium heat. Add the diced onion and bell peppers. Sauté for 6-8 minutes, until softened. Add the minced garlic and cook for 1 more minute until fragrant.

Step 2: Build the BBQ Chicken Filling
To the skillet with the sautéed vegetables, add the shredded chicken, BBQ sauce, drained black beans, drained corn, drained green chiles (if using), chicken broth, apple cider vinegar, smoked paprika, chili powder, and cumin. Stir until everything is thoroughly combined. Bring the mixture to a gentle simmer and let it cook for 5-7 minutes, allowing the flavors to meld and the sauce to thicken slightly. Season with salt and pepper to taste. Remove from heat.

Step 3: Assemble the Casserole Base
Pour the entire savory BBQ chicken filling into the prepared 9×13 inch baking dish. Spread it into a smooth, even layer. Set aside while you make the cornbread topping.

Step 4: Create the Ultimate Cornbread Batter
In a large mixing bowl, whisk together the dry ingredients: flour, cornmeal, sugar, baking powder, baking soda, and salt. In a separate medium bowl or large measuring cup, whisk together the wet ingredients: buttermilk, vegetable oil (or melted butter), and beaten eggs. Pour the wet ingredients into the dry ingredients. Add the entire can of cream-style corn. Gently stir with a spatula or wooden spoon until just combined. Do not overmix; a few lumps are perfectly fine. Overmixing leads to tough cornbread.

Step 5: Crown the Filling with Cornbread
Using a spatula or large spoon, carefully dollop the cornbread batter over the entire surface of the hot BBQ chicken filling. Gently spread the batter into an even layer, sealing it to the edges of the dish. The heat from the filling will begin to cook the bottom of the batter immediately, which helps create the perfect texture.

Step 6: Bake to Golden-Brown Perfection
Place the baking dish in the preheated oven. Bake for 25-30 minutes, or until the cornbread topping is fully set, deep golden brown, and a toothpick inserted into the center of the cornbread comes out clean or with just a few moist crumbs. The filling should be bubbling vigorously around the edges.

Step 7: Rest, Garnish, and Serve
Remove the casserole from the oven and let it rest for 10-15 minutes. This rest is crucial—it allows the filling to set slightly for clean serving and lets the cornbread finish steaming, ensuring it’s moist but not gummy. Garnish generously with sliced green onions and cilantro (if using). Drizzle with a little extra BBQ sauce for presentation. Serve warm, preferably with a pat of honey butter melting over each portion.