Put the grated sweet potato and the sliced onions ina large bowl. Add the chopped green chillies along with the coriander.
Add the chickpea flour along with the rice flour, nigella seeds, red chilli powder and salt and mix everything well with around 1/3 cup of water. Add enough water to make a sticky mixture which holds its shape and is not too watery.
Then add the chopped nuts and give it another mix.
Now take a little of the mixture and gently fashion them into small thin fritters and deep fry them till they are beautifully golden on all sides.
Garnish with a sprinkling of Chaat Masala, chopped cilantro and lemon wedges and serve hot.