Drain the chickpeas, add to a large pan with 400ml of water and season. Bring to the boil, then turn off the heat and set aside to allow the chickpea flavour to infuse the water.
Blitz the onions with the garlic, ginger and green chillies. Melt the ghee in a large saucepan, then add the onion mix with a pinch of salt and cook for 8-10 mins, until softened.
Stir in the spices, and cook for 3 more mins, adding a splash of the chickpea water to stop them sticking to the bottom of the pan. Add the tomatoes and another splash of water and cook for 5 mins, squishing the tomatoes with a spoon as they soften. Tip in the chickpeas, along with their cooking water. Cook for 10 mins. Season well, add the lemon juice, and a splash of water if you like a looser curry. Scatter with the coriander, to serve.