Place a 12-inch cast iron skillet (or oven-safe skillet) over medium heat. Add ground beef and cook until no longer pink, about 5 to 8 minutes. Drain excess grease.
While beef is cooking, dice the bell peppers. Then whisk together all the sauce ingredients in a mixing bowl. Set aside. Prepare cornbread batter and set aside.
Add the bell peppers and corn to skillet. Stir to combine. Pour in the sauce and stir everything together. Cook for 3 to 5 minutes until sauce thickens slightly. Remove from heat.
Sprinkle 1/2 cup shredded cheese over the sloppy joe mixture. Pour the cornbread batter over the cheese and then spread into an even layer over the top of the skillet. (Just do your best, it doesn't have to reach every nook and cranny of the top.) Sprinkle cornbread batter with remaining 1/2 cup cheese.
Bake for 15 to 20 minutes until the cornbread is set and the sloppy joe is bubbling. Carefully remove from the oven and let sit for 5 minutes. Sprinkle with parsley if desired. Serve warm. (We like our casserole with a dollop of sour cream!)
For a thick cornbread crust, use a 15-ounce package of mix. For a thinner crust, use an 8.5-ounce box of Jiffy cornbread mix.