Mix together yogurt and water in a bowl. Add rava and soak it for 10 minutes. The dough must bind well if it is dry you can sprinkle some water.
While the rava soaks, chop onions, chilies, curry leaves and coriander leaves. Grate ginger.
After 10 mins, add onions, chilies, leaves, cumin, salt and ginger to the soaked rava and make a dough. Beat the batter very well for 30 seconds to a minute with your hand in clock wise direction. This helps to make the rava vada fluffy. Lastly add soda and mix it gently.
The dough must bind well and must be sticky and easily spreadable. If it is dry you can sprinkle some water. If the dough is too stiff then they will turn hard.
Making rava vada
Heat oil in a deep fry pan. Grease a foil or cling wrap. Divide the dough to 12 portions and make balls. Place them on the foil. Flatten and make a whole in the center.
When the oil is just hot enough, test by adding a bit of the dough to the hot oil. The dough has to rise without browning. This is the right temperature.
Grease your fingers, transfer the vada to your fingers. Then gently shake off the fingers. Rava vada will drop in the oil. Do not disturb them for a while until they turn firm.
Fry until the rava vadas on a medium high flame by stirring often. Drain them on a kitchen tissue when they turn crisp & golden. Fry all the vadas in batches similarly. Serve rava vada with chutney.