Preheat your oven to 375°F (190°C) and prepare a baking sheet with foil or grease a loaf pan.

In a large bowl, combine ground beef, breadcrumbs, eggs, milk, onion, garlic, Worcestershire sauce, tomato paste, salt, black pepper, oregano, and basil. Mix until just combined.

Transfer half of the meat mixture into a loaf pan or shape it into a loaf on a surface. Create a trench down the center.

Fill the trench with shredded mozzarella or fresh mozzarella sticks, then cover with remaining meat mixture.

Mix ketchup, brown sugar, and balsamic vinegar for the glaze, then brush over the top of the meatloaf.

Bake for 50 to 60 minutes or until the internal temperature reaches 160°F (71°C). Tent with foil if browning too much.

Remove from oven, let rest for 10 minutes before slicing to allow juices to redistribute.

Slice and serve warm, garnished with parsley if desired.