Preheat oven to 400°.
In a mixing bowl, stir together the corn muffin mix, milk, and egg just until blended—the batter will be lumpy.
Coat the inside of a large 12-inch cast iron skillet with 1 tablespoon vegetable oil. Spoon batter into cast iron skillet. Set aside.
Add ground beef to a second skillet and cook over medium-high heat, stirring occasionally to break up the meat, until the beef is no longer pink. Remove beef to a plate lined with paper towels.
Add remaining tablespoon of oil and onion to the skillet, sauté until onion is tender, about 3 minutes. Add ground beef and seasoning packet and sauté 1 minute.
Stir in tomatoes, chilies, beans, and corn. Spoon mixture gently on top of the cornbread batter in the cast iron skillet.
Sprinkle cheese on top of tamale pie. Cover with foil and bake 25 minutes. Remove foil and broil until cheese begins to brown, about 5 minutes. Sprinkle parsley on top before serving.