Soak bread in lukewarm water. Peel onion and garlic and finely chop. Chop bacon finely and fry in 1 tablespoon oil. Sauté onion and garlic in bacon fat, remove from heat and let cool. Rinse parsley, shake dry and finely chop leaves. Add beef, bacon, egg, onion mixture, disengaged bread, salt and pepper to bowl and knead together.
Dice mozzarella. Forms meatballs from meat batter and flatten each. Add mozzarella cube to center of each meatball, cover mozzarella with meat batter and fry meatballs for 5 minutes on each side in remaining olive oil with butter over medium heat.