Dice papaya and any other fruit 2cm (except banana, leave that to the last minute so it doesn't go brown) and add to a large bowl with icing sugar and first measure of mint. Stir and set aside to marinate.
Add cream to a large bowl and use electric beaters to whip into soft peaks, about 3 minutes.
Place sponge on a tray with a lip and pour over ½-1 cup of soda per sponge, enough to soak the sponge but not too much or it will go soggy.
Tear sponge into bite-sized pieces and place half the sponge into a layer in the bottom of a trifle dish or deep glass bowl, or use mini bowls for a single serve option.
Layer with half the marinated fruit and top with half the cream. Repeat with remaining sponge, fruit (save a little for topping) and cream. Top cream with some decorative pieces of fruit, toasted nuts and mint leaves.