Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine the ground beef, ground pork, breadcrumbs, Parmesan cheese, chopped parsley, minced garlic, egg, salt, pepper, and Italian seasoning. Mix until just combined; do not overmix.
Take a small portion of the meat mixture, about the size of a golf ball, and flatten it in your palm. Place a cube of mozzarella in the center, then fold the meat around the cheese to completely enclose it. Roll it gently to form a smooth ball. Repeat this step until you have used all the meat mixture.
Place the formed meatballs on the prepared baking sheet, spacing them evenly. If desired, drizzle or brush a little olive oil over the top for extra crispiness.
Bake in the preheated oven for 25-30 minutes, or until the meatballs are cooked through and reach an internal temperature of 160°F (70°C).
While the meatballs are baking, heat the marinara sauce in a small saucepan until warm.
Once cooked, remove the meatballs from the oven and let them cool for a few minutes before serving. Serve with warm marinara sauce for dipping or pouring over the meatballs.