1. Preheat the oven to 425°.
2. Make the filling: Heat 1 tablespoon oil in a 10 1/2-inch cast iron skillet over medium heat until hot. Add the ground beef, onion, chili powder, salt, and garlic salt; cook until the beef is no longer pink, stirring frequently and breaking up any clumps of meat. Remove the beef mixture from the skillet to a bowl. Place the bell pepper rings in a single layer in the bottom of the skillet. Spoon the beef mixture over the rings.
3. Make the topping: Stir together the corn meal mix, cheese, sugar, salsa, milk, 3 tablespoons oil, and egg in a medium bowl; stir until well blended. Spread the batter evenly over the beef mixture in the skillet. Bake until golden brown, 32 to 38 minutes.
4. Place a serving plate over the skillet; carefully invert and remove the skillet. Cut into wedges. If desired, this can be served from the skillet: Cut into wedges and carefully turn each wedge upside down onto a serving plate.