Preheat the oven to 400°F. Warm the vegetable oil in the skillet over medium heat. Add the onion, bell pepper, broccoli, and seasonings. Stir to mix. Cover the skillet, reduce heat to "low," and let the veggies sweat until tender -- about 10 minutes.
Make the cornbread batter: In a medium bowl, whisk together the egg and buttermilk. Then add the packaged mix, and whisk to combine. Let sit for a minute or two while you finish the filling.
Sprinkle the ground meat as evenly as possible on top of the veggies. Spoon the cornbread mixture on top, and then spread it out to the edge of the skillet.
Bake in the preheated oven until the cornbread puffs and browns -- 25-30 minutes. Transfer to a wire rack and let cool for 5 minutes.
To unmold the dinner, first run a knife between the crust and the sides of the skillet. Remembering the skillet handle is red hot (use an oven mitt!) set a round plate or platter on top of the skillet, then invert and unmold. If any bits have stuck to the bottom of the skillet, simply scrape them up and return them to the top of the molded dinner. Serve hot, warm, or at room temperature.