Preheat your oven to 375°F (190°C).

In a large mixing bowl, combine the ground beef, ground pork, breadcrumbs, grated Parmesan cheese, egg, garlic powder, onion powder, oregano, salt, and pepper. Mix until fully incorporated.

Take a handful of the meat mixture, flatten it, place a cube of mozzarella in the center, and form into a meatball. Repeat until all mixture is used.

Heat olive oil in a large, ovenproof skillet over medium heat and brown the meatballs for about 5 minutes. Remove and set aside.

In the same skillet, add butter and chopped onion. Sauté until translucent, about 5 minutes.

Add minced garlic and stir for an additional minute until fragrant.

Sprinkle flour over the onion and garlic mixture and stir constantly for about 2 minutes.

Gradually add beef broth and Guinness while stirring to form a smooth sauce. Simmer for about 3 minutes until thickened.

Stir in Worcestershire sauce and nestle the browned meatballs into the gravy.

Bake in the preheated oven for 20-25 minutes until the meatballs are cooked through and the gravy is to your liking.

Let the skillet rest for 5-10 minutes before serving and garnish with fresh chopped parsley.