Heat the oven to 180°C.
Cut the squash into wedges, arrange them on a baking tray. Scatter the garlic cloves around ( in their skin), drizzle with 1 Tbsp olive oil then roast for about 30 minutes, until tender. Set aside.
Finally chop the onion and gently sauté in the remaining oil in a large saucepan.
Chop the courgette and tomatoes, then add to the onion. Cook for a couple of minutes, then add the spices and stir for 30 seconds.
Pour in most of the stock, bring to the boil, then cook for 10 minutes.
Remove & discard the skin of the roasted squash and garlic cloves, chop the flesh and add to the soup. Add more stock to cover the vegetables and cook for another 5 five minutes to warm through.
Turn off the heat. Add the fresh coriander leaves, then whizz with a stick blender until you get a thick, smooth soup. Add more stock, if you want the soup thinner.