Marinate fish with half of chilly powder, turmeric powder, salt and lemon juice for ten minutes and fry them for a few seconds. Remove from oil before it gets browned up. This is just to prevent it from breaking while cooking. Finely chop onions, green chillies, garlic and ginger( or you can use a kitchen chopper or food processor). Saute this along with curry leaves till golden brown in the same pan used for frying the fish. Add tomato puree and let it get cooked for two to three minutes or till the oil separates. Add chilly powder, turmeric, coriander, pepper and fenugreek and saute a another minute. Add one and one half cup of warm water and when it comes to a boil slide in the fried fish pieces and close lid. Cook in medium heat for seven to eight minutes. Finely add coriander leaves and simmer for a few second. Serve warm with rice.