In a large saucepan bring the water to a boil. Add the dahl, tomatoes, okra, carrots, potatoes, tumeric, salt and tamarind paste or lemon juice. Stir and bring back to a boil. Reduce the heat slightly and cook until the dahl is tender--approximately 30 minutes; add more water if necessary.
Meanwhile, in a heavy skillet, heat the oil and lightly fry the ground cilantro and cumin over a medium heat. Add the mustard seeds, chile and curry leaves and fry for 2 minutes, covering the skillet as the seeds pop. Add the fried spices to the cooked dahl and vegetables. Add the sambhar masala and mix well.
The stew can be prepared up to 2 hours in advance.
Recipe courtesy Everyday Epicurean by Catherine Bell (Ten Speed Press, 2000); Photograph by Kieran Scott