Cook basmati rice and yellow lentils together with water and salt until very soft.
Boil diced potato, carrot, and green peas until tender.
In a large pot, combine cooked rice-lentil mixture, boiled vegetables, tamarind paste, sambar powder, and 1 cup water; simmer for 10 minutes.
Heat ghee in a small pan, roast cashews and crackle mustard seeds.
Pour tempering over bisi bele bath, mix well, and serve hot with ghee.