In a large mixing bowl, combine beef, pork, Parmesan, eggs, salt, pepper, and seasoning. Add breadcrumbs ½ cup at a time until the mixture is not too wet and can be formed into balls easily. Form 12 balls, and place onto prepared cookie sheet
For each of the balls, press a hole into the center. add the mozzarella into the hole, then close it by pressing the meatball mixture around the cheese.
Heat a large saute pan over medium heat, and drizzle olive oil into it. When the oil is shimmering, add meatballs and cook until just browned (not that depending on the size of your pan, you may need to do this in batches). Using a slotted spoon or tongs, transfer the meatballs into the slow cooker.
Pour marinara sauce over the browned meatballs, then set the slow cooker to low, and cook for 5 hours.
Enjoy over pasta or on their own!