If you want a vegetarian dish to make an impact on the table, this does the job - it looks great and has really complex flavours.
- Heat the oven to to 220C/425F/gas mark 7. Put the squash and onions in a large bowl, add three tablespoons of oil, a teaspoon of salt and some black pepper, and toss well. Spread, skin down, on a baking sheet and roast for 40 minutes until the vegetables have taken on some colour and are cooked through. Keep an eye on the onions: they may cook faster than the squash, so may need to be removed earlier. Remove from the oven and leave to cool.
- Put the tahini in a small bowl with the lemon juice, water, garlic and a quarter-teaspoon of salt. Whisk to the consistency of honey, adding more water or tahini as necessary.
- Pour the remaining oil into a small frying pan on a medium-low heat. Add the pine nuts and half a teaspoon of salt, cook for two minutes, stirring, until the nuts are golden brown, then tip the nuts and oil into a small bowl.
- To serve, spread the vegetables on a platter and drizzle over the sauce. Scatter the pine nuts and oil on top, followed by the za'atar and parsley.