Drain the soaked dal and grind it with ginger, garlic, green chili, fennel, and cumin seeds into a coarse paste(reserve 1 tsp of soaked chana dal for later use)
Remove the dal mix from the blender and add 1 tsp of soaked chana dal, onion, coriander leaves, cut banana flower, and salt, and combine everything together
Now take a ball size vada mix and press gently to get a flat shape and keep it aside
In a pan heat the oil and fry the vadai in medium heat until it turns golden brown in color and remove the vadai from the oil and drain it
Repeat the same process for the rest of the vadai
Serve
Serve the warm Vazhaipoo vadai with a hot cup of tea or coffee