In a very clean pestle and mortar, bash most of the mint leaves with the finely grated lime zest. Add the sugar, a good lug of rum and the lime juice, then mix again gently. Have a taste and add a touch more sugar if you think you need to, but bear in mind the fruit may be quite sweet.
Toss the fruit together in a bowl with a little of the mojito mixture, then spread it all out on a big plate. Spoon the rest of the mixture over the top, decorate with a few torn-up mint leaves and serve.