In a large bowl, mix together beef mince, breadcrumbs, garlic, parsley, parmesan cheese, salt and pepper until fully combined. Form mixture into 3cm balls and place onto a baking sheet lined with parchment paper. Bake for 20 minutes or until golden brown.
Meanwhile, heat olive oil in a large pot over medium heat. Add onion and garlic and cook until softened, about 5 minutes. Add passata and oregano to the pot and bring to a boil. Reduce heat to low and simmer for 20 minutes or until sauce is thickened. Season with salt and pepper to taste.
Bring a large pot of salted water to a boil and cook spaghetti according to package instructions, stirring occasionally until al dente. Drain pasta and return to the pot.
Add olive oil, butter and parmesan cheese to the pot and mix everything together. Serve with meatballs on top and enjoy!