Grind the chutney. Put the grated coconut, dried Byadagi chillies, garlic, tamarind and salt into a grinder. Add a small amount of water and grind to a smooth, thick paste. Scrape down the sides as needed, adding water gradually rather than all at once.
Check the seasoning. Transfer to a bowl. Taste and adjust the salt and consistency to your liking.
Make the tempering. Heat the coconut oil in a small pan. Add the mustard seeds and let them splutter, then add the curry leaves briefly.
Finish and serve. Pour the hot tempering over the chutney and mix. Serve with hot idlis, dosas or Nesal Pundi.