Preheat the oven to 400 degrees F (200 degrees C).

Heat oil in a Dutch oven over medium heat. Add chicken. Cook, stirring occasionally, until no longer pink inside, 5 to 7 minutes. Add carrots, celery, bell pepper, and scallions and cook until tender, about 5 minutes. Add tomatoes, black beans, chili powder, cumin, garlic, onion powder, paprika, salt, and black pepper. Stir to combine. Cook until heated through, about 5 minutes more.

While mixture simmers, combine cornbread mix with milk and egg in a bowl.

Remove Dutch oven from heat and spread cornbread batter on top of chicken mixture to form the crust.

Place Dutch oven in the preheated oven and bake until cornbread is golden and beginning to brown, 20 to 25 minutes.