Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large mixing bowl, combine ground beef, ground pork, breadcrumbs, Parmesan, egg, garlic, oregano, salt, pepper, and parsley.
Mix by hand until ingredients are just incorporated, avoiding overworking the proteins.
Portion the mixture into approximately 1.5-ounce segments (about 12-16 total).
Flatten each portion into a disc, place one mozzarella cube in the center, and wrap the meat around the cheese.
Roll between palms to form a seamless sphere, ensuring the cheese is fully encapsulated to prevent leakage during cooking.
Arrange meatballs on the prepared baking sheet with at least 1 inch of space between each.
Bake for 18 to 20 minutes, or until the internal temperature reaches 160°F (71°C).
Heat marinara sauce in a wide skillet over medium heat.
Transfer cooked meatballs into the sauce and simmer for 2 minutes to glaze before serving.