Preheat the oven
Heat the oven to 350� F and line a baking sheet with parchment paper so the pockets crisp instead of sticking. Set the tray within easy reach, because the filled pockets will go straight onto it once assembled.
Wash the vegetables
Rinse the Onion, Green Bell Pepper, Red Bell Pepper, and Fresh Parsley if using. Pat everything dry well so the filling does not turn watery in the pan.
Chop the filling vegetables
Peel the onion and finely chop it. Cut the green bell pepper and red bell pepper in half, remove the stems and seeds, then finely chop both so they cook quickly and tuck neatly into the pockets. Roughly chop the parsley into small flecks for stirring in at the end. If your Corn is canned, drain it well; if it was frozen, make sure it is fully thawed and not icy.
Brown the beef
Set a large skillet over medium heat. Add the Butter and let it melt, then add the Ground Beef. Cook, breaking the meat up with a spoon or spatula, until it loses its raw color and starts to brown in small craggy bits, about 6 to 8 minutes. Stir often so the beef cooks evenly and the butter coats the pan.
Cook and season filling
Add the chopped onion to the beef and cook for 2 to 3 minutes, stirring often, until it begins to soften. If the onion released a lot of liquid while chopping, squeeze or blot off the excess before it goes in. Stir in the chopped green bell pepper, red bell pepper, corn, Salt, Black Pepper, and Paprika (or chili flakes). Cook for 4 to 5 minutes, stirring, until the peppers soften, the corn is heated through, and the mixture smells fragrant. If using parsley, stir it in right at the end.
Cool the filling
Take the pan off the heat and let the filling sit for 5 minutes so it cools slightly and becomes easier to handle. Warm filling is fine, but very hot filling can soften the flatbreads too much while you assemble.
Fill and fold pockets
Lightly sprinkle or mist the Flatbreads (large, thin) with a little water to make them flexible, then cut each flatbread in half. Spoon some of the beef filling onto one side of each piece, leaving a small border around the edge. Top with Shredded Mozzarella, then fold each piece over into a triangle pocket and press the edges gently to seal as well as possible. Arrange the pockets on the lined baking sheet, and if you have a little extra mozzarella, scatter some over the tops for extra browning.
Bake until crisp
Bake the pockets for 20 to 25 minutes, until the outside is deeply golden and crisp and the cheese inside has melted. Let them rest for 5 minutes before serving so the filling settles and the crust stays crunchy instead of tearing open with steam.
