1. Preheat the oven to 375°F and line a baking sheet with parchment paper.

2. Cook the spaghetti in salted boiling water until al dente, then drain and set aside.

3. Heat olive oil in a skillet over medium heat. Add the ground beef or Italian sausage and cook until browned, breaking it apart as it cooks.

4. Stir in the marinara sauce, salt, black pepper, Italian seasoning, and crushed red pepper flakes if using. Simmer for 5 minutes.

5. Add the cooked spaghetti to the sauce and toss until well coated.

6. Slice the tops off the bread bowls and hollow out the centers, leaving sturdy sides and bottoms.

7. Mix melted butter with minced garlic, parsley, and a little Parmesan cheese.

8. Brush the garlic butter inside each bread bowl and around the cut edges.

9. Bake the empty bread bowls for 5 minutes to lightly toast them.

10. Fill each bread bowl with saucy spaghetti.

11. Top with mozzarella cheese and the remaining Parmesan cheese.

12. Bake for 12 to 15 minutes, until the cheese is melted and bubbly and the bread edges are golden.

13. Garnish with extra parsley and serve warm.