Bring a pot of salted water to a boil. Add the spaghetti and cook according to the package instructions or until al dente. Reserve a cup of pasta water, then drain and set aside.

Finely chop the 1/4 onion and mince the garlic clove.

In a large skillet, heat the olive oil over medium heat. Add the chopped onion and minced garlic, sauté until the onion becomes translucent, about 3-4 minutes.

Add the ground beef to the skillet, breaking it apart with a spoon. Cook until the beef is browned and cooked through, about 5-7 minutes. Season with salt and pepper to taste.

Pour in the marinara sauce and stir well to combine. Allow the sauce to simmer for about 5 minutes. If the sauce is too thick, you can add a bit of the reserved pasta water to achieve the desired consistency.

Add the cooked spaghetti to the skillet with the sauce and toss to coat evenly. Allow it to heat through for about 2-3 minutes.

Serve the Spaghetti Bolognese hot, garnished with grated Parmesan cheese if desired.