In a pressure cooker, combine the toor dal, turmeric, red chilli powder, salt, shallots and tomato. Add water just upto its level. Cook for one whistle. Allow the pressure to go by itself.
In a chatti (earthern pot), add the sambar vegetables with little salt and water upto its level. Bring it to boil and cook till almost done.
Pour in the prepared lentil mixture. Add the sambar powder. Squeeze in the tamarind juice - add more water if the tamarind still has its juice. Give a good mix.
Add the jaggery as well, and simmer for a few minutes till the flavors are done. Adjust seasoning and switch off.
For tempering, heat coconut oil. Splutter mustard seeds, add the rest of the ingredients. Fry briefly and add into the sambar.
Allow the sambar to rest till serving. The more it sits, the better it tastes.