Wash Urad dal and Moong/Chana dal. Soak them in water for 4-5 hours or the entire night.
Take out Dal from water and wash once them more. Grind wet Dal without adding water or just a little water. There should be very less water in it. Do not grind Dal into a very fine paste.
Put in salt,ginger, green chilli and green Dhaniya(coriander) to the grounded Dal then blend these well. The more you beat Dal it gets more soft. The mixture required to prepare Sambhar Vada is ready.
You can give shape to this mixture using your hands or a plastic sheet. In southern India banana leaves are also used in place of plastic sheets.
Pour oil in a pan(kadhai) and heat, wet fingers in water. Place 1 or 1 2/2 tbsp of mixture on the wet fingers and using your thumb or the fingers of the other hand make a crater into a hole. Put this Vada in hot oil to fry, according to the oil in the pan make 3-4 Vadas and put them in one go. Turn over the Vada when its lower side turns brown. Fry till both sides turn brown then take it out. Similarly, take out all the Vadas. All of your Vadas are ready.
Before serving put Vadas in hot Sambhar(How to make Sambhar?) and enjoy its unique taste.