Combine the ground lentil paste with ginger, chillis and salt. Whip well to incorporate a lot of air into the batter.
Pre-heat oil in a deep frying vessel on medium heat. When hot, place a sheet of plastic wrap in your palm and place a little batter and shape into a big lemon sized ball and drop slowly into the hot oil. Continue adding balls to the oil until no more space. Deep fry on medium heat for 10 minutes and then fry on high heat till golden brown.
Remove these deep fried vadas from the hot oil and place them into a bowl of luke warm water. Leave them in it for 15-20 seconds. Remove and gently press between your palms so that excess water oozes out. Keep them aside.
Finish making vadas with the rest of the remaining batter and put them in water like you did for the earlier batch, remove excess water and keep aside.
Add the water, red chilli powder, cumin powder and salt to the yogurt.
Place the vadas on a baking sheet and pour the yogurt mixture evenly all over the vadas, covering them completely. Chill the vadas for sometime before serving. At the time of serving, take 2-3 vadas and place them in a serving plate and sprinkle some chaat powder and garnish with cilantro leaves and tamarind chutney.