Add the urad dal, red chillies and asafetida. Fry until urad dal changes color slightly. Don't let it burn.
In a bowl, combine coconut, onion, tamarind paste and salt.
Add the red chilli mixture to the rest of the ingredients.
Grind until smooth adding as little water as possible (a traditional Indian mixer is better at this than a blender or food processor).
If desired, you may add tempering.
Tempering - In a small pan, heat oil then add black mustard seeds, curry leaves and red chillies. When mustard seeds splutter, add to the chutney and mix well.
Depending upon what kind of onion you use, the smell of raw onions may be overpowering. If that is the case, after tempering, heat 1 tsp oil in a pan and fry the chutney for about 10 min until all the raw smell is gone.