Wash and add water about 2 times more of the dal, along with turmeric and hing. Pressure cook till the dal is cooked. Except rice and tamarind water, add the chopped vegetables, spices, salt along with 5 cups of water.
Cover the pan with the lid without the whistle, so that it starts boiling. Then, add the rice and simmer for 5 mins. Then, add the extracted tamarind water and cook with lid covered. Pressure cook it for 3 whistles.
Once the pressure is off, heat a pan with ghee and splutter mustard seeds, then sauté onions, curry leaves. Then, add the cashew nuts.
Pour this ghee over the sambar rice.
This goes well with appalam or papad with some poriyal if you have time.