Preheat your oven to 375°F (190°C).
In a large mixing bowl, combine the cooked spaghetti and marinara sauce. Mix well until the spaghetti is evenly coated.
Slice the Italian loaf of bread in half lengthwise, then hollow out the center of each half to create a boat for the spaghetti.
In a separate bowl, mix the melted butter, minced garlic, dried parsley, dried oregano, salt, and pepper.
Brush the garlic butter mixture generously onto each half of the hollowed bread.
Fill each half with the spaghetti mixture, ensuring it’s packed in well.
Top the spaghetti with shredded mozzarella cheese, and sprinkle with Parmesan cheese if desired.
Place the stuffed bread halves on a baking sheet, and cover loosely with aluminum foil.
Bake in the preheated oven for 15 minutes, then remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and slightly golden.
Remove from the oven and let cool for a few minutes. Slice into pieces and serve warm.