Halve and deseed the grapes. Mark the orange skins into quarters and peel as for eating. Scrape away all white pith and then cut the oranges downwards through the centre, first in half and then in quarters. Cut the orange quarters across into chunky pieces so that each bit has a minimum amount of skin attached. Peel and slice the bananas.
Mix all the fruits together with the dressing. Add the chopped mint and pile into crisp lettuce leaves for serving.