In a frying pan, heat sunflower oil and shallow fry the marinated fish. Fry on both sides till fish turns golden brown in color.
Note: Over frying will make the fish very hard, so be careful that you do not overdo the frying.
In a mixer, powder the cashew nuts without adding any water. Once powdered, add 2tbsp of the thin coconutmilk and grind till it is in a thick paste form. Check consistency and add one more tbsp if required.
Heat oil in a small pan and add tomato pieces and salt. Saute till tomato blends well. Keep this aside.
Heat oil in a wok and splutter mustard seeds. Saute onions till translucent. Do not over fry the onions.
Next add the fried fish to the wok. Cover and cook for 10-15 minutes.
Add the previously sauted tomato to the wok. Mix well and cook for 10 minutes.
Add the thick coconutmilk and the thick cashew nut paste. Mix well.
Add curry leaves, crushed cardamom and cinnamon stick. Cover and cook for 10 minutes.
:- The consistency of this curry should be slightly thick and not very watery. If it is too watery, open and cook for some more time till the gravy dries up a little.