Heat a large frying pan with a generous amount of oil until smoking hot. Add the aubergines and fry, stirring occasionally, until browned. Turn the heat to low and simmer until tender. Season with chilli powder and salt to taste.
Tip the aubergines into a colander and leave to drain for 10 minutes.
Meanwhile, to make the salsa, mix the mango with the mint, lime juice and chilli.
Heat a grill to medium and grill the prawns until pink and cooked, turning halfway.
Return the aubergines to the frying pan on a medium heat. Fold in the ketchup, mustard and lemon juice. Simmer for 3–4 minutes. Meanwhile, toast the coconut chips in a heavy-bottomed frying pan over a medium–high heat until aromatic.
Stir the spring onions and toasted coconut chips into the aubergine mix. Divide between six plates alongside the mango salsa. Top each portion with a tiger prawn and serve.