In a bowl, mix 1tsp turmeric powder, 1tsp red chili powder, 2tbsp lemon juice, 2tbsp corn flour and 1tsp salt with fish pieces.keep in refregartaor for 30 minutes.
Heat 1/4cup oil in a pan and place fish pieces and fry both sides till golden. Remove them & keep aside.
Heat oil in another pan, add whole garam masala and Allow it to splutter.
Then add onion paste, tomato puree, ginger garlic paste, cumin&coriander powder, garam masala powder and yogurt. Add ¼ cup water, 1 tsp salt, turmeric powder, red chili powder and mix them well. Cook it for 5 minutes until mixing all the ingredients properly and oil separates.
Then add the fried fishes and a cup of hot water. Cover and Simmer the gravy on low flame for about 15 minutes. Turn off the heat.
Remove only the cooked fish pieces form gravy and set aside.
Add 2 litre water, 1tbs oil, green chilies, ginger paste and whole garam masala in a deep bowl. Heat the bowl and let it boil.
Wash rice and drain all water.
Now pour rice into the boiling water and cook on medium heat for 8 minutes or till it is 70% cooked. Drain water and keep aside.
Now take a heavy bowl,spread 1tbsp ghee and spread half of the rice. Now take fish masala gravy and spread evenly over rice. Sprinkle 1/2 fried onions, mint and coriander leaves and Spread 1 tbsp ghee on top.
Again spread 1/2 cooked rice over the gravy, sprinkle 1tbsp ghee, food color and some fried onions on top of the rice. Cover the lid tightly and cook for 15 minutes on low heat.
Turn off the heat, mix rice with masala.
Take fish slices and place over the biryani before serving.