1. Cook the spaghetti in a large pot of salted boiling water until al dente. Reserve 1 cup of pasta water, then drain and set aside.
2. In a large bowl, combine ground beef, breadcrumbs, Parmesan cheese, egg, garlic, onion, parsley, salt, pepper, and Italian seasoning. Mix until just combined.
3. Form the mixture into meatballs, about 1 to 1.5 inches in diameter, and place on a baking sheet.
4. In a skillet, heat olive oil over medium heat. Cook meatballs in batches until browned on all sides, about 5-7 minutes. Transfer to a plate.