Preheat oven to 400°. Place 5 (6-inch) cast-iron skillets on a large rimmed baking sheet lined with parchment paper. Spray skillets with cooking spray.
In a medium bowl, stir together self-rising flour, ½ cup cheese, cornmeal, sugar, and 1 teaspoon salt. Using a pastry blender, cut in cold butter until mixture is crumbly. Stir in buttermilk until a smooth batter forms.
In a 10-inch cast-iron skillet, heat oil over medium-high heat. Add onion and bell pepper; cook until tender, about 3 minutes. Add garlic; cook until fragrant, about 1 minute. Whisk in all-purpose flour until smooth; cook for 1 minute. Whisk in milk; cook until slightly thickened, about 3 minutes. Add chili powder, ½ teaspoon pepper, cumin, coriander, remaining 2 cups cheese, and remaining 2 teaspoons salt, whisking until cheese is melted. Stir in chicken, beans, tomatoes, chiles, and cilantro. Divide chicken mixture among prepared skillets. Drop batter by spoonfuls over chicken. Bake until tops are golden brown, 25 to 30 minutes; serve warm.
Recipe by Southern Cast Iron at https://southerncastiron.com/mexican-chicken-pot-pies/