In a large saucepan, heat oil; cook onion and garlic, stirring, until onion softens.
Add beef to pan; cook, stirring, until browned. Add paste, stock and tomatoes; bring to the boil. Reduce heat; simmer, covered, 30 minutes. Uncover; simmer a further 45 minutes or until sauce is thickened. Remove from heat; stir in oregano. Season to taste.
Meanwhile, in a large saucepan of boiling water, cook pasta in until tender; drain.
Serve 6 cups of the bolognese mixture with the pasta, sprinkle bowls of pasta with parmesan.
Reserve and freeze remaining bolognese for later use.