Soak the tamarind in water and squeeze well to extract the juice and set aside.
Pressure cook the rinsed moong dal with water for 3 whistles. Mash the cooked dal and set aside.
Add the onion pieces, tomato pieces, chopped / cubed radish and water in a vessel. COver with a lid and cook till the radish pieces are soft.
Add the mashed dal, tamarind extract, salt, sambar powder, turmeric powder, jaggery and water (adjust to desired consistency) to the vegetables.
Allow the sambar to boil for 8 – 10 minutes.
If the sambar appears too thick, add little more water and simmer for a few minutes.
Heat oil in a pan for seasoning. Add the mustard seeds and cumin seeds and let them splutter.
Then add the curry leaves, red chilli and hing and fry for a couple of seconds. Add this to the sambar and mix.
Serve hot with rice or idli / dosa.