Peel and cut the raw banana into round shapes.
Put them in water to prevent them from darkening.
Soak tamarind and extract the juice.
Heat oil in a wok.
Add mustard seeds and black gram.
When the mustard seed splutter, add the onions and fry, till it turns pink.
Drain the raw banana and add it to the wok.
Add the tamarind juice, turmeric powder, sambar powder, salt and 1/2 cup water.
Cover the pan and allow it to cook.
When the banana is cooked, add the coconut milk and bring it to boil.
:- Serve hot with rice.