Marinate the fish with above mentioned ingredients for 2-3 hours in the fridge.
Heat oil in a frying pan and shallow fry fish from both sides and set aside to add to the gravy which you will make in step 2.
Step 2 Method:
In a separate pan, add chopped onions and fry till light brown.
Add in Fenugreek seeds and fry 30 to 40 seconds, followed by whole red chilis and fry for 10-20 seconds, followed by Curry leaves and fry for another 10 seconds.
Now add garlic paste and turmeric powder and give it a stir.
Add National Fish Masala and chopped tomatoes and fry till 1 to 2 minutes and then tomato puree and cook for 8 to 10 minutes on a very light flame till the gravy and oil separates.
At this stage add cream and butter and leave to cook for 5-7 minutes on a low flame.
Add the fried fish very gently, cover the lid and cook for another 5 minutes. Adjust salt at this step.
Fish curry is ready now garnish it with chopped coriander & julienne ginger.