1) In a small pot place coconut milk, ginger, chilli and zest. Bring to a simmer for 3 or 4 minutes. Remove and cool. Then remove the ginger slices. 2)Stir the yoghurt into coconut milk. Season with salt and pepper. 3)Fold through fish, prawns and lime juice. 4)Place cos lettuce in the bases of 4-6 glasses. Spoon the fish over. 5)Garnish with mint leaves and chilli slices. Place a lime slice on the side of each glass.