Preheat oven to 375°F (190°C).

In a large mixing bowl, combine the ground beef, Italian breadcrumbs, grated Parmesan cheese, milk, eggs, finely diced yellow onion, minced garlic, chopped fresh parsley, dried oregano, salt, and black pepper.

Using your hands, gently mix all ingredients until just combined. Be careful not to overmix, as this can make the meatloaf tough.

Press about half of the meatloaf mixture evenly into the bottom of a 9x5 inch loaf pan.

Arrange the thinly sliced or shredded mozzarella cheese over the first layer of meatloaf, leaving a small border around the edges.

Carefully top with the remaining meatloaf mixture, pressing it gently to seal the mozzarella completely and form a cohesive loaf.

In a small saucepan, combine the ketchup, brown sugar, apple cider vinegar, and Worcestershire sauce. Heat over medium-low heat, stirring until the brown sugar is dissolved and the glaze is smooth.

Pour about two-thirds of the glaze evenly over the top of the meatloaf in the pan.

Place the loaf pan on a baking sheet (to catch any potential drips) and bake in the preheated oven for 50 minutes.

After 50 minutes, remove the meatloaf from the oven and spread the remaining glaze over the top. Return to the oven and continue baking for another 15-20 minutes, or until the internal temperature reaches 160°F (71°C) when measured with a meat thermometer.

Once cooked, remove the meatloaf from the oven and let it rest in the pan for 10-15 minutes before slicing. This allows the juices to redistribute, ensuring a moister meatloaf. Slice and serve warm.