Heat olive oil in a large pan over medium heat, then add onion, carrot, and celery. Cook until softened.
Add garlic and stir for another minute before adding the minced beef. Cook until browned all over.
Stir in tomato paste, canned tomatoes, and oregano. Season with salt and black pepper.
Reduce heat and let the sauce simmer gently for about 30 minutes, stirring now and then.
Meanwhile, cook the spaghetti according to package directions until al dente.
Drain the pasta, divide into bowls, and top with the Bolognese sauce.
Sprinkle with parmesan and garnish with basil if you like.