In a bowl, combine ground beef, breadcrumbs, Parmesan, egg, minced garlic, salt, pepper, and Italian herbs. Mix until evenly combined but do not overmix.
Form the mixture into 1-inch meatballs. Set aside.
Heat olive oil in a skillet over medium heat, using enough to coat the bottom of the skillet. Add meatballs and cook until browned on all sides, about 8-10 minutes. Remove meatballs and set aside.
In the same skillet, sauté onions until translucent, adding more oil if needed. Add marinara sauce and bring to a simmer.
Return meatballs to the skillet with the sauce, cover, and simmer for 20 minutes, or until the meatballs are thoroughly cooked.
While the meatballs are simmering, cook spaghetti in a large pot of salted boiling water according to package instructions until al dente. Drain.
Toss the cooked spaghetti with the meatball sauce. Serve hot, garnished with extra Parmesan and fresh basil.