Preheat the oven to 160°C. Put 1tbsp of olive oil in a large ovenproof casserole or tagine. Cut aubergine and squash into chunks and fry over a medium-low heat until slightly softened.
Add the onion and garlic and fry until translucent. Add ras el hanout, harissa and whole chilli peppers, and fry for 1-2 mins until fragrant.
Add cinnamon, passata, preserved lemons, juice of the lemon, honey, stock and cardamoms. Season with salt and pepper, cover and put in the oven for 1 hour.
Remove from the oven. Add the olives and remove the chillies, cinnamon stick, preserved lemons and serve with couscous and pitta bread.