Cut the eggplant / aubergine in to 2-3 cm (1 inch) cubes.
In a large mixing bowl combine 1 tablespoon salt with 120ml (½ cup) hot water and stir until the salt dissolves.
Mix in 360ml (1½ c) cold water, then add the eggplant / aubergine cubes.
Stir to coat the eggplant, then weigh it down with a plate and leave to soak for 30 minutes.
Preheat the oven to 200˚C fan / 220˚C / 392˚F convection / 428˚F.
Line a baking tray with baking parchment.
Drain the aubergine and pat dry, then place on the lined baking tray and mix with 3 tablespoons of olive oil.
Place in the preheated oven and roast for 20-30 minutes, until the aubergine / eggplant is golden, turning halfway through.
If you want firmer, slightly crispy chickpeas, drain and pat dry, then add to the aubergine / eggplant 10 minutes before the aubergine is due to be ready.
Whilst the eggplant is roasting, make the sauce: fry the sliced onion in 2 tablespoons olive oil over a low-medium heat until soft and caramalized - around 15 minutes.
Add the crushed garlic, cinnamon, ground cumin and chilli powder and cook for 2 minutes.
Add the roughly chopped tomatoes and 2 tablespoons of water and simmer for 5-10 minutes until thick, adding a little more water if it seems to thick.
Stir in the roasted eggplant and chickpeas (either roasted or from the can) and simmer gently for 5 minutes.
Check for seasoning, adding a little more salt if needed.
Serve at room temperature or cold.
Will keep in the fridge for up to 3 days, or cool completely and freeze.