Preheat your oven to 400°F (200°C).
In a large mixing bowl, combine ground beef, breadcrumbs, Parmesan, parsley, egg, garlic, salt, pepper, and oregano.
Shape the mixture into meatballs, about 1.5 inches in diameter, and place them on a baking sheet lined with parchment paper.
Bake the meatballs in the preheated oven for 20 minutes, or until browned and cooked through.
While the meatballs are baking, boil a large pot of salted water and cook the spaghetti according to package instructions until al dente.
In a large skillet, warm the marinara sauce over medium heat, stirring occasionally.
Once the meatballs are cooked, carefully transfer them to the skillet with the marinara sauce.
Toss the cooked spaghetti with the marinara sauce and meatballs until well coated.
Serve the spaghetti and meatballs hot, topped with additional grated Parmesan cheese and fresh parsley if desired.