In a medium size mixing bowl, combine rice flour, sooji and all-purpose flour. Add yogurt and salt. Mix well making sure that there are no lumps. Set aside for at least 30 minutes.
When ready to make dosas, mix cumin seeds, green chilies and chopped cilantro in the batter.
Heat a tawa or griddle on medium-high flame. Pour batter using a ladle from about 3"-4" above the tawa in a circular motion from outside to the center. Don't spread the batter.
Pour 1~2tsp oil on the batter and cook until golden brown and crispy, about 3~4 minutes per side.
Grind onions, tamarind paste, dry red chilies, salt and the garlic into a coarse paste.
Heat 1tbsp oil in a pan, add mustard and cumin seeds and once the seeds start to splutter, add the ground paste. Cook on medium flame stirring frequently until the raw smell of onions goes away, about 8~10 minutes.
Serve with idli, dosa, upma or even with plain rice.