Add the red onion, ginger, garlic, green chilies and cilantro to a blender jar.
Blend for a minute until you get a chunky mixture.
Add the soaked lentils to the same jar and blend for a couple of minutes.
You should get a slightly coarse mixture that looks like this. Mix in the spices and salt.
Heat oil in a pot and use a spoon or your fingers to drop small balls of the prepared mixture into it.
Let them cook on medium heat for a few minutes until golden brown and crispy.
Notes
Drain most of the water from soaking and then blend the moong dal. You should ideally have a batter that's thick but soft.
If the batter seems too thick, add a splash of water to get it to the right consistency.
If the batter has become too thin, add some semolina (rava) to the batter and let it rest for a few minutes before you fry the fritters.
Make sure the oil is hot enough before you start adding the vada mixture into it, or the vadas will end up soaking a lot of oil.
To check if the oil is hot enough, add a drop of the vada mixture into it. If it sizzles immediately, the oil is ready!
Cook the vadas on medium heat until golden brown, and place them on paper towels to remove any excess oil.
To get the perfect soft vadas, whisk the batter vigorously until it turns slightly light in color. This helps incorporate air into the batter which makes it more fluffy.