Heat 1tbsp oil in a large saute pan. Add the tempering ingredients and when the seeds start to splutter, add the onions and cook till they start to get brown around the edges.
Next add the tamarind paste, turmeric, sambar powder, jaggery/ sugar and salt. Mix well. Add a splash of water if the mixture looks too dry. Cook for 1~2 minutes.
Stir in the chopped idlis and cook for 2~3 minutes. Turn off the heat and sprinkle the chopped cilantro. Serve right away.