Preheat the oven to 160° fan/180°C/gas mark 4.
Soak the chipotle chilies in freshly boiled water for 20 minutes to soften.
Tip the chopped onion into a large, heavy saucepan with a lid. Add 1 tbsp of the olive oil and cook over a low–medium heat for about 8 minutes until softened and just starting to brown at the edges.
Meanwhile, cut a cross on the underside of each tomato and soak in a bowl of freshly boiled water for 1 minute to loosen the skins. Drain the tomatoes under cold running water, peel off the skins, cut out the tough core and roughly chop the flesh. Set aside.
Combine the aubergine and peppers in a large roasting tin, drizzle with the remaining olive oil and mix thoroughly to coat the vegetables in oil. Cook in the oven for about 30 minutes, turning every 10 minutes, until softened and golden brown.
Add the garlic and cumin to the onions and cook for another minute. Drain the chipotle chilies, finely chop and add to the saucepan with the tomato purée. Stir to combine and cook for a further 2 minutes to lightly caramelize the tomato purée.
Add the chopped tomatoes, chickpeas and vegetable stock and season well with salt and freshly ground black pepper. Bring to the boil, reduce the heat and simmer for 10 minutes until the tomatoes have broken down and softened.
Add the roasted aubergines and peppers to the pan, cover and continue to cook for a further 10 minutes until the aubergines are very soft and have soaked up the tomato sauce. Add the date syrup and adjust the seasoning if needed. Scatter with the coriander and lemon zest to serve.