Preheat the oven to 350°F and grease a meatloaf pan with cooking spray or vegetable shortening. If using a standard loaf pan instead of a meatloaf pan, I highly suggest lining with parchment paper. Set aside.
In a large mixing bowl, combine the onion, garlic, seasoned bread crumbs, eggs, Parmesan cheese, milk, Worcestershire sauce and salt.
Add the ground meatloaf mix to the large mixing bowl, breaking apart into smaller pieces as you go. Gently toss with your hands until evenly combined, some bits of bread crumb mixture might still be visible, that is okay.
Take half of the meat mixture and press it into the loaf pan and slightly up the sides. Place the mozzarella cheese in a mound down the center and then cover all around and top with remaining meat mixture, packing it down snuggly.
Place in the oven, uncovered for 30 minutes.
Meanwhile, in a small saucepan, combine the ketchup and grape jelly. Stir over medium-high heat until it has combined. Remove the meatloaf at the 30 minutes mark and pour over top, returning back to the oven uncovered.
Bake for an additional 25-30 minutes or until the internal temperature reads 160°F.
Remove and allow to rest for 5-10 minutes before carefully removing from the pan and slicing to eat.
Notes
I put my onion and garlic in a small food processor and then made it into a paste.