Heat your oven to 220°C/Fan 200°C/Gas 7. Halve the squash. Scoop out the seeds. Peel and slice into chunks around 1 cm across. Pop it on a baking tray. Drizzle with 1 tbsp olive oil. Season with salt and pepper. Roast for 30 mins till tender.
Finely slice the salami into strips around ½ cm wide. Rinse the watercress and pick off any thick stalks. Pat the watercress dry. Peel and finely slice the onion. Fill a kettle and boil it.
Warm a 1/2 tbsp olive oil in a frying pan. Add the salami. Fry over a medium-high heat for 1-2 mins till the salami is just starting to crisp up. Lift out of the pan. Pop on a plate lined with kitchen paper to drain. Take the pan off the heat.
Fill a pan with hot water from the kettle. Bring to the boil. Add the penne. Simmer for around 8 mins till the penne is cooked but not too soft. Drain.
While the penne cooks, put the frying pan back on a lowish heat. Add the onion. Season. Fry for 5-8 mins till the onion is soft and golden. Stir every so often so it doesn't catch.
Add the roast squash to the onion. Add the drained penne, the salami and the watercress to the pan. Stir to mix everything together till the watercress just starts to wilt.
Divide the squashy penne between two warm plates or bowls. Grate on as much Parmesan as you like to serve.