Heat olive oil in a medium pan over medium heat. Add chopped onion and sauté for about 5 minutes until translucent. Stir in minced garlic, crushed tomatoes, bay leaf, and black pepper. Simmer for 20-30 minutes until thickened.

Preheat your oven to 400°F (200°C).

In a large bowl, combine lean ground pork, lean ground beef, egg, Italian seasoning, salt, black pepper, and chopped parsley. Mix thoroughly but do not overmix.

Take a portion of the meat mixture, flatten it, place a cube of mozzarella in the center, and mold the meat around the cheese.

Arrange the meatballs on a lined baking sheet, leaving space between them. Bake for 15-20 minutes until cooked through and golden.

Serve warm meatballs over marinara sauce, garnished with extra parsley or basil.