Marinate the washed fish pieces with lemon juice and salt and keep aside for 15 minutes.
Heat a nonstick saucepan over medium-high heat until hot.
Add oil and swirl to coat the bottom.
Add mustard seeds, when it splutter, add curry leaves, pepper corns and sliced onions .
Stir and cook for 1 minute till the onions are soft and translucent.
Add ginger, green chillies and garlic and stir till the garlic are cooked and then add turmeric and stir.
Slowly slide in fish pieces and cook for a minute.
Lower the flame on simmer and add enough salt.
Swirl the pan with your hand to distribute the salt (this helps to keep the fish pieces intact).
Add coconut milk and simmer for 10 minutes.
Switch off the flame and add lemon juice.
:- Transfer to a serving plate and garnish with curry leaves!!!