Half boil the potatoes, peel and chop them into large peices.
Heat oil. Splutter the mustard seeds. Add the urad dal and fry for a few seconds.
Add the red chillies, hing and turmeric and saute for around 15 seconds.
Add the chopped potatoes, green chillies, curry leaves and coriander leaves and mix well.
Add 1/2 cup water and bring to boil. Sprinkle salt and cook on low flame till done.
Keep on high flame and saute till the water is all dried up. Even if the potatoes break up, it's fine.
Add the coconut and give a final mix. Switch off and serve as side dish with rice or with pooris.