Measure the water into a large saucepan and bring to a boil. Add the rice and salt, reduce heat to low, cover and simmer for 20 minutes or until rice is tender and the water has been absorbed.
Heat 1/2 tablespoon of oil in a small skillet set over medium heat. Add the cashews and toast until fragrant, about 5 minutes. Remove from the heat and set aside.
Heat the remaining oil in the same skillet over medium heat. Add the chile peppers, mustard seeds and cumin seeds. Once the seeds start to pop, add the curry leaves and half of the nuts. Cook and stir until fragrant, about 3 minutes. Remove from the heat.
When the rice is done, transfer it to a serving bowl and stir in the turmeric, lime juice and tamarind paste, then mix in the chilies and spices along with the oil from the skillet. Garnish with the remaining nuts and serve with plain yogurt on the side.