Grind the grated coconut, fried gram, green chillies, garlic, curry leaves, coriander, cumin and tamarind with salt and a little water. Keep it slightly coarse or grind smooth, as you prefer.
Check the seasoning. Add more water after grinding if you want a thinner chutney to pour around your idlis or vadas.
Heat a little oil in a small pan. Add mustard seeds and let them splutter, then add the urad dal. Once it is golden, add the broken dried red chilli briefly.
Pour the tempering over the chutney and mix. Serve with steaming idlis or vadas.