Add oil, onion, carrot, celery and garlic to the slow cooker. Cut steak into quarters and add to slow cooker along with passata, stock, oregano and bay leaves.
In a small bowl, whisk together cornflour and water thoroughly to combine and add to slow cooker. Season to taste with salt and pepper and stir to combine.
Cover and cook on low heat for 6 hours. Remove lid and saute, uncovered, for 30 minutes. Remove and discard bay leaves.
Remove beef and shred using two forks. Return to slow cooker, stirring to combine with the sauce.
Meanwhile, bring a large pot of water to the boil and season generously with salt. Cook pasta according to packet instructions. Drain.
Toss pasta with sauce and divide between six serving bowls. Serve with parmesan cheese and parsley.
