Put the ingredients for the chermoula into a mini food processor and blend into a smooth paste. Preheat the oven to 220°C, fan 200°C, gas 7.
Cut each carrot into 4 chunky pieces. Cut the butternut squash into small chunky wedges and the courgettes diagonally into 2.5cm thick slices.
Heat the oil in a large casserole pan. Add the onion and carrots. Cover and cook gently over a medium heat for 5 minutes, until the onion is soft but not browned. Uncover and add half the preserved lemon, 2 tablespoons of the chermoula paste, the stock, honey, tomatoes, butternut squash, potatoes and ½ tsp of salt. Bring to the boil, cover with foil and a close-fitting lid, and transfer to the oven. Cook for 45 minutes, then remove the casserole dish from the oven and lower the temperature to 180°C, fan 160°C, gas 4. Stir the courgettes and chickpeas into the tagine, then cover and return to the oven. Cook for a further 30 minutes, or until all the vegetables are tender.
Stir the rest of the chermoula paste and preserved lemon into the tagine and adjust the seasoning to taste. Scatter with the black olives and mint leaves and serve with some buttered couscous.
To cook in the slow cooker
Use 500ml stock (instead of 750ml). When all the ingredients are brought to the boil, transfer to a 6.5-litre slow cooker and cook for 2 hours on high. Add the chickpeas and courgettes and cook for a further 1 hour on high. Add the remaining chermoula and preserved lemon, olives and mint and serve straight away.