Trim the spring onions, carrot and celery. Chop all the vegetables, chillies (stalks removed) and sausages. Add to large frying pan on a high heat with a lug of olive oil, fennel seeds and oregano, breaking it up and stirring as you go. Keep checking on it and stirring while you get on with other jobs.
Fill a large deep saucepan with boiling water. Season well then add the penne and cook according to packet instructions, with the lid askew.
Crush the unpeeled cloves of garlic into the sausage mixture and stir in the balsamic vinegar and the tinned tomatoes. Add a little of the starchy cooking water from the pasta to loosen if needed.
Drain the pasta, reserving about a wineglass worth of the cooking water. Tip the pasta into the pan of sauce and give it a gentle stir, adding enough of the cooking water to bring it to a silky consistency. Taste, correct the seasoning, then tip into a large serving bowl and take straight to the table with the Parmesan for grating over.
