Mix the rice flour and besan with salt and chilli powder. Now toss in the sliced onions, green chillies, curry leaves and mix this.
In a small bowl, mix the 4 tsps of oil with the baking soda thoroughly. Add this to the onion-flour mixture and combine.
Heat the oil to deep fry the pakodas and when it''s at the right temperature (test by dropping a small piece, it should sizzle, fry and float up immediately), take a batch from the onion-flour mixture and add as little water as possible to just dampen and hold it together.
Now drop this batch into the hot oil (as small pieces) and deep fry till crisp and golden. Drain on paper towels and serve hot. Repeat this with the remaining onion-flour mixture, remembering to dampen each portion just before dropping them in oil.