Sauté prawns in oil and keep aside. Sprinkle a pinch of salt while sautéing. To the same pan add oil. As the oil heats up add black pepper corns and let them crackle. To this add the onion paste and let it become translucent. To this add ginger and garlic paste and green chillies. Cook till golden brown. Add the powdered spices to this and cook for another 5-7 mins. Add shrimps and stir fry for another 5 mins. Add salt to taste. Finally add coconut milk to the pan. Allow to simmer. You can add water to your choice for the consistency of the gravy.