Soak tamarind in the 1 to 2 cups of water, squeeze the pulp out of it and keep aside.
Wash the toor dal well and cook in a pressure cooker or in a sauce pan till mushy.
Place the tamarind pulp in a heavy bottomed pan on the stove. Add all the vegetables, except tomatoes. Add more water, if needed.
Add turmeric powder and cover and cook, till the vegetables are cooked well.
Add the tomatoes and let it cook though as well. Add salt and keep heat on low.
To make the ground paste:
Meanwhile, heat the oil in a saute pan and dry roast the spices. Add the coconut to it and roast till coconut slightly turns color. Don't let it brown a lot.
Let it cool. Grind to a very fine paste in a food processor or an Indian mixie, adding very little water occasionally.
Now add this mixture to the vegetables in tamarind sauce and let it come to a boil.
Mash the cooked dal well and add it to this. Let it cook for a couple of minutes.
Heat the oil for tempering in a saute pan. Add the mustard seeds. Once they splutter, add curry leaves and pour it over the sambar.
Switch off the heat for the sambar. Add some minced cilantro at the very end.