Prepare the Bread: Preheat your oven to 375°F (190°C). Slice the top third off the loaf of bread and scoop out the interior, leaving about 1/2 inch of bread on the sides and bottom to create a bowl.

Cook the Meat: In a skillet over medium heat, add olive oil and sauté onions and garlic until translucent. Add ground beef and cook until browned. Drain any excess fat. Stir in marinara sauce, oregano, basil, salt, and pepper. Cook for another 2-3 minutes.

Assemble the Stuffing: In a mixing bowl, combine the cooked meat mixture, shredded mozzarella cheese, grated Parmesan cheese, and egg. Mix until well combined.

Stuff the Bread: Fill the hollowed bread with half of the meat mixture. Add a layer of pepperoni slices. Fill with the remaining meat mixture and top with more mozzarella cheese.

Bake: Place the filled bread on a baking sheet and bake for 20-25 minutes, or until the cheese is melted and bubbly.

Serve: Let it cool for a few minutes, slice, and garnish with fresh parsley if desired.