Drain all the water from soaked dal.Reserve a tablespoon of whole dal and rest grind to a paste without water (preferably little grainy paste).
In a small coffee grinder put curry leaves,coriander leaves,chillies,cumin seeds,fennel seeds,ginger and garlic.grind to a coarse paste(Don't add any water to it while grinding).
In a big bowl mix dal paste,reserved whole dal,rava,rice flour,the spice paste,chopped onions,salt and mix well.
Heat oil in a deep pan to. Take small portions of the mixture and make into patties.Put into the oil and fry in medium heat until both sides are nicely brown.
In the meantime dry roast coriander seeds and dry red chilli(try not to burn).In a mortar and pestal crush along with a pinch of salt and make a coarse powder.
While serving sprinkle the vadas with the spice powder.