Malabar Fish Biryani

For 8 people. To Marinate the fish: King Fish- 3 lb (5 big slices)or 1 1/4 kg Red chili powder- 3 tsp Turmeric-2 tsp Lemon Juice-2 tsp Salt to taste Canola/Vegetable Oil -3/4 cup or as needed for frying the fish. For the Masala: Onion –6 medium ones(including one for garn..