Bring a large pot of salted water to a boil. Add the spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.
While the pasta cooks, heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until soft and translucent, about 5 minutes.
Add the minced garlic to the skillet and cook for 1 minute until fragrant, stirring frequently to avoid burning.
Pour in the crushed tomatoes, then stir in dried oregano, dried basil, salt, black pepper, and red pepper flakes. Simmer the sauce over low heat for 15 minutes, stirring occasionally.
Stir the cooked spaghetti into the sauce until well coated. Remove from heat and mix in grated Parmesan cheese and chopped fresh parsley.
Preheat the oven to 375°F (190°C).
In a small bowl, combine the softened butter, minced garlic, chopped parsley, and salt to make the garlic butter spread.
Slice the Italian bread loaf in half lengthwise. Spread the garlic butter mixture evenly over the cut sides of the bread.
Place the bread halves on a baking sheet, cut side up, and bake in the preheated oven for 10-12 minutes, or until the bread is golden and crispy.
Remove the garlic bread from the oven and let it cool slightly. Cut into slices.
Serve the pasta topped with extra Parmesan cheese if desired, alongside warm garlic bread.