Put the chickpeas in a pan, cover with cold water and bring to the boil. Boil vigorously for 10 minutes, then reduce the heat so that the water boils steadily and cook for 1-1 1/2 hours.
Meanwhile, make the sauce. Set 2 tsp of the garlic aside and place the remainder in a food processor. Add the onion, ginger and half the chillies. Pour in 75ml of the water and process to a smooth paste.
Heat the oil in a large stock pot and cook the cumin seeds for 30 seconds. Stir in the coriander seeds, turmeric, chilli powder and ground cashew nuts. Add the ginger and chilli paste and cook, stirring frequently, until the water begins to evaporate. Add the tomatoes and stir-fry until the mixture begins to turn red-brown in colour.
Drain the chickpeas and add to the pan with the parsnips and remaining water. Season with 1 tsp salt and black pepper. Bring to the boil, stir, then simmer uncovered, for 15-20 minutes until the parsnips are completely tender.
Thicken the liquid by boiling until the sauce is reduced. Add the toasted cumin seeds and lime juice to taste. Stir in the reserved garlic and chilli and heat through and serve.