Cook tuvar dal in the pressure cooker till it can be mashed (3 whistles). Heat the oil and put jeera and mustard seeds and asfoetida.
When they start spluttering put the finely cut onions and saute them.
Wash curry leaves cut them into small pieces and put them along with the onions. Then put tomatoes, finely grated mooli and very small pieces of ginger. Mix them with the spoon and keep on the gas for 5 mins till the mooli becomes soft. Put the sambhar powder, red chilli powder and salt.
Then add the the tamarind water and put the dal and boil it for 15 mins constantly stirring it.