Cut the gelatin sheet into strips, then soak them for 10 minutes in a flat dish, filled with about 3-5 Tbspful of water.
Meanwhile, peel & chop the mango, then whizz in a blender until you get a smooth purée.
Heat 40 ml of water with the sugar in a heavy-based pan. When the sugar has dissolved add the drained gelatin strips. Once the gelatin has also dissolved, turn off the heat.
Pour this syrup into the mango purée. Add most of the lime zest and the coconut milk, then whizz for a few seconds.
Pour this mixture into 4 small dessert dishes, silicon moulds or cups and chill for 2-3 hours, until set.
Serve with the remaining lime zest sprinkled on the top.