Soak the cumin seeds, fennel seeds and bay levaes in warm water for 2 odd hours. Drain from water, grind to a smooth paste.
Marinate the fish with the masala paste (from the last step), onion paste, ginger paste, green chilli paste, turmeric powder, red chilli powder and 1 tbsp mustard oil. Keep aside, some 30 minutes or so.
Heat the remaining oil in a heavy bottomed pan, throw in the fenugreek seeds . Allow the seeds to splutter. Once the fenugreek seeds have released their aroma, carefully discard the fenugreek seeds from the hot oil.
Gently place the fish in the oil, pour in the remaining marinate, give it a gentle mix. Sauté for a couple of minutes.
Throw in the green chillies, add a sprinkle of salt. Cover and cook till the fish is cooked and oil starts to separate from the masala.
Adjust seasonings, rest for 15 minutes. Serve hot.