Dry roast the cumin seeds and fenugreek seeds till lightly brown about a minute or so.
Grind this roasted seeds along with the grated coconut and onion to a paste and set aside.
In a large enough pan, add the oil, fish and rest of the ingredients green chilly, tomatoes, tamarind juice, turmeric powder, red chili powder, salt, coriander leaves, dill leaves and the onion-coconut paste.
Add a cup of water and mix well.
Cook on medium to low flame stirring occasionally. Just rotate the pan gently and don't stir too hard with the spoon. The fish breaks easily if you stir too much.
Switch off the flame when the green chili changes it's color and oil starts floating on top.