Preheat the oven to 200°C/Fan 180°C/Gas 6. Put the butternut squash, onions and garlic into a roasting tin and mist with cooking spray. Season to taste and roast for 20 minutes, then remove the garlic and turn the vegetables over.
Return to the oven and roast for another 15-20 minutes until the vegetables are tender and golden.
Meanwhile, cook the couscous to pack instructions and set aside. Put the tahini, lemon juice and agave syrup into a mini blender or food processor with 2 tbsps cold water.
Squeeze the roasted garlic cloves from their skins into a food processor, then blitz until smooth. Set aside.
Toss the couscous with most of the herbs and divide between bowls. Top with the roasted butternut squash and onions, followed by the peppers and sun-dried tomatoes.
Drizzle over the tahini dressing and scatter over the lemon zest and extra herbs, then serve.