Meatball Sub Homemade "Hot Pockets"

Preheat oven to 350 degrees F and line two baking sheet with parchment paper. Make meatballs: In a large bowl, combine ground beef, bread crumbs, garlic, parsley, and crushed red pepper flakes and season with salt and pepper. Roll into meatballs and transfer to one prepared baking sheet. Bake until browned and cooked through, 15 minutes. Let cool, then break up into smaller pieces. On a floured work surface, roll out pie crust into a large rectangle and slice off rounded edges (if using store-bought). Slice into four strips. Spoon marinara, meatballs, and mozzarella onto bottom halves of pie crust strips and fold over tops. Use your fingers to pinch to seal and press the twines of a fork to crimp. Brush with egg wash and transfer to prepared baking sheet. Bake until golden and puffy, 18 to 20 minutes.