In a coffee grinder or mortar and pestle , crush ginger, garlic and green chillies. Heat oil in a pan and add mustard seeds. When they pop, add diced onion, crushed ginger, garlic and green chilies.
Make a paste with chili, coriander and turmeric powder by adding a little water and add to the pan. Combine it well.
Add sliced mango pieces, salt and toss it for a minute.
Pour thin coconut milk to the pan and add prawns. Mix it well.
Cover it with a lid and let it cook on a medium flame for 6-7 minutes.
Remove the lid, add thick coconut milk and curry leaves and mix it well.
Let it stand on fire for 2 minutes and remove. Serve hot with rice!!!!