1. Preheat oven to 375°F (190°C).

2. Bring a large pot of salted water to a boil. Cook spaghetti noodles until al dente, then drain and set aside.

3. In a large skillet over medium heat, add olive oil and sauté diced onion for 2-3 minutes. Add garlic and cook 1 minute more.

4. Add ground beef to the skillet. Cook until browned, breaking up the meat with a spoon. Drain excess fat.

5. Stir in marinara sauce and Italian seasoning. Let simmer for 5 minutes. Taste and add salt and pepper as needed.

6. In a large bowl, toss the cooked spaghetti with 1 cup of the meat sauce.

7. Transfer spaghetti to a greased 9×13-inch baking dish.

8. Pour remaining meat sauce over the spaghetti in an even layer.

9. Sprinkle mozzarella cheese and parmesan cheese evenly over the top.

10. Bake uncovered for 25-30 minutes, until cheese is bubbly and golden brown.

11. Let cool for 10 minutes, then garnish with chopped parsley if desired. Slice and serve.