Rinse and pat dry the prawns. Heat 1 tbsp coconut oil in a pan and add the coconut, chopped onion and fennel seeds. Saute over a medium heat until the coconut is golden . Remove and grind to a smooth paste in a blender.
Heat 2 tbsps coconut oil in the pan and add the sliced onion and fry until translucent. Add the green chillies and the ginger garlic paste and saute for 2-3 minutes. Stir in the ground spices and half of the mango strips.
Add the prawns and salt to the pan and cook, stirring, until they are opaque and almost cooked. Stir in the coconut paste, coconut milk and the remaining mango. Simmer gently until the prawns are just cooked.
Meanwhile heat the remaining 1 tbsp of coconut oil in a seperate pan and saute the fenugreek seeds, mustard seeds and curry leaves until aromatic.
Serve the prawn curry topped with the aromatic spice mixture and green mango strips. Accompany with rice or Indian bread.