1. Cook the spaghetti according to the package instructions until it reaches that perfect al dente texture. Drain the spaghetti well and set it aside.

2. In a large skillet, brown the ground beef with the diced onion over medium heat. Drain any excess fat, then add the tomato sauce, tomato paste, Italian seasoning, salt, and pepper. Let the sauce simmer for about 5 minutes.

3. Toss the cooked spaghetti into the savory meat sauce, ensuring every strand is coated.

4. Preheat your oven to 375°F. Slice the Italian bread loaf in half lengthwise and hollow out some of the bread interior.

5. Mix together softened butter and garlic powder until well combined. Spread this mixture over the cut sides of the bread.

6. Toast the prepared bread halves in the preheated oven for 5-7 minutes, or until lightly crisp and golden brown.

7. Spoon the spaghetti and meat sauce mixture into the hollowed-out bread halves, distributing it evenly. Top with shredded mozzarella cheese and sprinkle with grated Parmesan cheese.

8. Place on a baking sheet and bake for 10-12 minutes, or until the cheese is melted and starting to brown.

9. Slice into generous portions and serve hot.