Clean the fish and fillet it. ( Fillet it means slicing the flesh from the bone as a full fillet)
you will be having four fillets now.
Marinate with little turmeric, salt and lemon juice
Peel and slice the ripe mangoes, cut into strips and place it in the cut side of fillet and roll it tightly and tie it with a banana plant string or spring onion keep aside.
For the ground masala-
Grind together the coconut, half the mango,shallots, tomato, turmeric, chilli powder into a smooth paste.
Slice the left over mango. Slit the green chilli. Peel and slice the ginger into juliennes.
Heat little oil in a pan and fry the fish rolls for a while and remove.
Heat the same oil, splutter curry leaves, fry the ginger and green chilly. Add fenugreek powder and quick fry for a second.
Add the coconut paste to the pan and simmer for few minutes. Add salt, mango pieces and fish rolls. Simmer in slow flame till the fish has cooked through. Remove from fire.
For tempering- Heat oil, splutter mustard, curry leaves, sprinkle the chilly powder and quickly remove from fire and pour over the fish.
Serve hot with steamed rice.