In a pressure cooker add the nakai, baking powder and 2 cups of water and cook for 3-4 whistles. (this will help to soften the nakai). When the pressure has released, drain the nakai, reserving the liquid.
Heat oil in a wide pan. When the oil is hot, add cumin seeds, black mustard seedsand green cardamom pods. Fry unti fragrant.
Add the sliced onions and fry until the onions brown on the edges. Add garlic, chilli and curry leaves and fry for a further 30 - 45 secs.
Add the masala, turmeric and 1 tablespoon of water. Saute, stirring often until the oil separates.
Add the drained nakai, salt to taste and cook stir well. Add ¼ cup of the reserved, drained liquid.
Reduce the heat to low and cook covered for 10 mins, adding more reserved liquid if necessary.
Remove lid and cook until all the liquid has evaporated and the oil separated from the nakai.
Garnish with coriander and a wedge of lime or lemon.
Serve with roti or rice and dahl.