Preheat the oven to 400 degrees F. Line a large baking sheet with parchment paper and set aside.
Heat a large non stick skillet over medium high heat, add the oil, and then cook the ground beef, stirring occasionally, for about 4-5 minutes.
Stir in the taco seasoning mix until combined. Let cook for 2 minutes and stir in the vinegar.
Let cook for about 2 minutes or until vinegar has almost evaporated. Reserve.
In a medium bowl, combine the onion, corn, black beans, tomatoes, and cilantro . Season with a pinch of salt and pepper if desired. Reserve.
Unroll all pie crusts on a lightly floured surface according to the directions on the package. Equally divide each crust into fourths.
Next, trim all edges to form rectangles. Use all the trimmings to make a ball of dough, roll out on a floured surface, and cut into 4 rectangles.
You will end up with a total of 20 rectangles. Reserve.
Using 1/4 cup as measure, fill the measuring cup a third of the way full each with the following three components: cooked ground beef, vegetable mixture, and cheese, respectively.
Place contents of the filled 1/4 cup measure onto the center of one rectangle. Repeat the process for the other 9 rectangles.
Make sure that there is at least a 1/2-inch margin from the edges of the rectangle. Sprinkle salt and pepper on top of the mixture if desired.
Brush the edges of the crust with the egg wash, then fold the empty side of the crust over the top of the filling.
Pinch your fingers along the edges to seal and then use a fork to make marks all the way around.
Transfer the 10 hand pies to the lined baking sheet and brush the top of each tart with more egg wash. Sprinkle a bit of salt and pepper on top if desired.
Bake for 10-12 minutes, then rotate the baking sheet 180˚.
Bake another 2-3 minutes or until the crust is lightly golden brown.
Let cool for 5-10 minutes on the baking pan, then remove hand pies with a large spatula and serve by themselves or with sour cream and guacamole.