Spread the grated coconut on a baking sheet and roast till lightly toasted. With a mortar and pestle or food processor, grind the toasted coconut with the peppercorns and 1/2 cup water to a coarse paste. Set aside.
Heat the oil in a deep pot and add the mustard seeds. When they burst, add the onions and fry for 1 to 2 minutes until soft and transparent.
Add the green chillies, curry leaves, and ginger and garlic pastes and fry for a minute, Then add the chopped tomatoes. Stir-fry for one more minute, until the tomatoes are soft. Add the chilli powder, coriander and turmeric and stir-fry till the oil rises to the top.
Add the ground coconut paste and continue stirring for 1 to 2 minutes.
Add the water, salt, soaked chickpeas. Stir, cover with a lid and simmer for 30 to 40 minutes, until the gravy has thickened and the chickpeas are tender.