1.
Put a kettle of water on to boil. Put the beans into a saucepan, cover with boiling water and simmer for 6 minutes. Drain and rinse the beans, then drain again.
2.
Dice the cheese into a shallow salad bowl; add the beans.
3.
To make the dressing, halve the lemon and squeeze one half to give 2 tablespoons juice. Mix with the olive oil, then peel the garlic and crush it into the dressing. Chop enough mint to give 2 tablespoons, and put a few sprigs aside for a garnish. Whisk the chopped mint into the dressing, then add salt and black pepper to taste.
4.
Arrange the prawns in the bowl and pour over the dressing. Serve with mint sprigs and wedges cut from the remaining half lemon.