To prepare crust, preheat oven to 275 F. Stir together egg whites, sugar and vanilla until sugar has half dissolved. Stir in coconut until evenly coated with egg mixture. Grease a 10-x-4-inch rectangular tart tin and spoon coconut mixture into it. Press filling into pan, pressing into bottom and up sides of each cup (dip your fingers in a cup of cool water while doing this to prevent the mixture from sticking to your fingers). Bake for 35 to 45 minutes, rotating pan halfway through baking. Shells will be a rich golden brown around edges. Allow to cool in pan then remove.
To prepare mousse, cream mascarpone gently with sugar to soften. Add lime zest, lime juice and mango pulp and stir until evenly blended (switch to a whisk if you wish, but be careful not to over beat). If mousse is too soft, chill for 20 minutes to firm up. Pipe or spoon mousse into coconut tart shell and chill until ready to serve.
Garnish with a selection of tropical fruits immediately before serving. The tropical fruits can be sliced ahead of time, and stored under a damp cloth until ready to garnish.