Peel the oranges, removing all the white pith. Holding each orange in turn over a large bowl, cut between the membranes to release the segments, letting them fall into the bowl with the orange juice.
Using a long serrated knife, cut the top and bottom off the pineapple, then cut off the peel. Halve the pineapple lengthways. Place one half, cut-side down, on a cutting board and cut lengthways into three equal sections. Slice off the hard core from each section, then cut the sections crossways into chunks about 2.5cm thick. Add to the oranges in the bowl and toss. Repeat with the other half of the pineapple.
Slice the bananas 5mm thick and add immediately to the other fruit and juice in the bowl. Toss to coat. Gently fold in the marshmallows and coconut. Cover with plastic wrap and chill for at least 2 hours or overnight to blend the flavours (if chilling overnight, add the banana just before serving). Garnish with mint sprigs.
Some more ideas…
*Use chopped apples instead of the oranges. *For an adult's only flavour, add 1 tbsp dark rum to the orange juice. *Add black grapes for more colour. Halve 1 cup (170g) seedless grapes and toss in with the oranges, pineapple and banana. *You can use large marshmallows instead of the miniature ones, if you prefer.
The fruits in this dish are high in bioflavonoids, substances with anti-oxidant properties that prevent tumour growth and help keep arteries healthy. Plus, there's as much fibre per serving as in a bowl of wholegrain breakfast cereal.