Roasted Winter Squash with Tahini

I have a love for Ottolenghi's vegetable dishes and this one, made by my eldest son, is excellent.  The tahini dressing could probably be used to dress quite a number of roasted vegetables (I have used it with zucchini and it is just as fabulous).

2 lb.  squash, cut into 1 x 2 inch pieces 
2 red onions, cut into 1inch wedges 
 3 Tbs. olive oil
  salt and black pepper
3½ tbsp. Tahini
1½ tbsp lemon juice
3 tbsp water
1 small garlic clove, crushed 
 1/4 c. toasted nuts
1 tbsp. za'atar
1 tbsp roughly chopped parsley

Heat the oven to 425F. 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 color 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.