Cut the aubergine lengthwise, then slice it into crescent-shaped strips. Cut the onion in half, then thinly slice.
Heat 3 Tbsp oil in a large saucepan, add the aubergine and a pinch of salt, then cook until softened. When it starts browning transfer to a plate.
Heat the remaining oil, fry the onion until soft, add the garlic and stir for a minute.
Meanwhile, remove the flesh of the preserved lemon and cut the skin into thin strips.
Add the lemon peel strips and spices to the onion, stir for one minute. Stir in the chopped tomatoes, chickpeas, sugar and half of the coriander. Season with salt and pepper. If too thick, add some water - about 100 ml.
Bring to the simmer and cook for 10 minutes. Taste it - if necessary, add more sugar, salt or pepper.
Stir through the fried aubergine slices, cook gently for 5 minutes.
Serve with the remaining coriander leaves scattered on the top.