In a bowl, mix the flours, baking powder, salt, turmeric, cumin, coriander and chilli powder.
Add the onion, chillies, sweetcorn and fresh coriander.
Slowly add water and mix until you get a thick batter. It should drop off a spoon but not be runny.
Heat oil over medium heat. Test by dropping a tiny bit of batter in. It should sizzle and rise.
Spoon tablespoons of batter into the oil. Don’t overcrowd.
Fry until golden brown, turning occasionally, about 3–4 minutes.
Remove and drain on paper towel. Serve hot.