1. Preheat your oven to 350°F (175°C).
2. If using French bread, hollow out the center, leaving about a 1/2 inch border. If using frozen bread dough, roll it out and shape it into a loaf sturdy enough to hold the filling.
3. Prepare your spaghetti or angel hair pasta by cooking it according to the package instructions. Drain the pasta and set it aside, cutting the spaghetti into manageable lengths if desired.
4. In a skillet, heat olive oil over medium heat. Sauté chopped onions and garlic until fragrant and translucent. Add ground beef or Italian sausage and cook until browned.
5. Pour marinara sauce into the skillet with the meat. Add Italian seasoning and allow the mixture to simmer until thickened slightly.
6. Combine softened butter, minced garlic, and Italian seasoning to create the garlic spread. Mix until evenly incorporated.
7. Place the hollowed-out bread on a baking sheet. Spread the garlic butter mixture on the inside and over the surface of the bread.
8. Fill the bread cavity with the cooked spaghetti, layering it evenly. Top the pasta with the seasoned marinara and meat sauce.
9. Sprinkle shredded mozzarella cheese generously over the sauce, ensuring full coverage.
10. Bake the assembled bread subs in the preheated oven for 15-20 minutes (French bread) or about 35 minutes (frozen dough) until the cheese is melted, bubbly, and golden brown.
11. Remove the subs from the oven and allow them to cool slightly before slicing.
12. Garnish the subs with fresh parsley or basil for added flavor and presentation.
13. Serve immediately and enjoy your Spaghetti Stuffed Garlic Bread Subs as a delicious meal or snack.