Wash and soak the lentils in water for about 2 hours.
Clean and remove the flowers from the stalk. You can refer to my post here on how to clean and remove the flowers. Chop them into fine pieces and keep them immersed in diluted buttermilk until ready to use. To make the diluted buttermilk, mix the yogurt in about 3 cups of water and use.
In a food processor, add the soaked and drained lentils, green chilies, red chilies, salt, and asafetida, and pulse a few times to make a coarse paste.
Now add the chopped vazhaipoo (drain well before adding), onion, cilantro, and fennel seeds, and pulse a couple of times to combine.
Remove the vadai batter in a bowl and add the curry leaves. Mix well.
Meanwhile, heat the oil to deep fry the vadais. Make small balls out of the batter and flatten it slightly. Gently slide it into hot oil and fry until golden brown. Do not have the flame too high as the vadai will become too dark on the outside and the inside will remain raw.
Drain them on a paper towel-lined bowl and serve hot with chutney or sauce.