Preheat oven to 250C (480F).
Place pumpkin pieces in a deep baking tray and spray lightly with oil to coat. Bake for 10 minutes then add the eggplant and zucchini (also sprayed lightly with oil). Roast for a further 20 minutes or until cooked. Remove from oven and set aside.
Combine the couscous and boiling water in a bowl, mix with a fork, cover with plastic wrap and let stand for 7 minutes.
To make the dressing place all ingredients in an airtight jar and shake until combined.
Loosen the couscous with a fork until light and fluffy. Add the roast vegetables, onion, capsicum and spinach leaves. Mix the dressing through the salad until coated.