Adjust oven rack to the middle position and preheat the oven to 450 degrees F.
For the Tamale Filling:
Heat the oil in a 12-inch skillet over medium heat until shimmering. Add the onion, chili powder, and 1/2 teaspoon salt and cook until the onion is softened, about 5 minutes. Stir in the garlic and cook until fragrant, about 30 seconds.
Stir in the beans and tomatoes and bring to a simmer. Stir in the pulled pork, cheese and cilantro and season with salt and pepper to taste. Pour the tamale filling into the bottom of a 9-inch pie plate.
For the Cornbread Topping:
In a medium bowl, whisk the flour, cornmeal, sugar, baking powder, baking soda, and salt together. In a separate bowl, whisk the buttermilk and egg together. Stir the buttermilk mixture into the flour mixture until uniform. Stir in the butter until just combined.
Dollop the cornbread batter evenly over the filling and spread into an even layer. Bake until the cornbread is cooked through in the center, 10 to 15 minutes. Serve.