Preheat the oven to 180°C.
Cut the onion into wedges, the pepper into large chinks, the cauliflower into small florets.
Arrange these in a baking dish, then tuck the garlic cloves between them.
Mix the harissa, tomato purée, lemon juice and cumin seeds. Rub this into the veggies, then season to taste. Roast in the oven for about 25-30 minutes, until soft and lightly charred.
Take the tin out of the oven and let the veggies cool a bit, then remove the skins of the onion and garlic (and the pepper skin too, if preferred). You can chill the vegetables until you’re ready to make the soup or carry on now.
Transfer the vegetables to a saucepan. Add the cooking jus too (maybe rinsing the roasting tin with some water). Add the stock and bring to the boil.
Cook for 5 minutes, then add half of the chickpeas and the herbs.
Using a stick blender, blitz the soup until smooth. Add more stock if it’s too thick.
Add the remaining chickpeas, reheat if needed, then serve.