Soak the tamarind in water and squeeze well to extract the juice and set aside.
Pressure cook the rinsed moong and pigeon lentils with 2 cups water for 3 whistles or boil in 5 cups of water till it’s cooked. Mash the cooked dal and set aside.
Heat oil in a pot, add in the mustard seeds, fenugreek seeds and let them splutter. Add in the asafoetida and cumin seeds. Add in half of the curry leaves, onions and garlic. Saute for 2-3 minutes.
Now add in the potatoes, radish, drumsticks, and cook till the potatoes are halfway cooked. Now add in the red chilli powder, sambar masala and salt.
Saute for 2 more minutes. Now add the mashed lentils, jaggery, tomatoes, tamarind and water.
Boil the sambar for 5 minutes and then add the green peas and let it boil for another for 5 minutes. Garnish with coriander and serve hot with idlis.