Remove the seeds from the melon with a teaspoon. Using a sharp knife mark the flesh into small cubes, then carefully cut off the skin into a bowl. Cut each grape in half and add them with the lime juice, gently mixing to combine.
Spoon into a glass serving dish and add the yoghurt, then tear over enough of the mint leaves to your taste before serving.
Bring the prepared melon and grapes in an airtight container with the mint leaves sitting on top and a lime already halved to squeeze over before serving. Put the yoghurt in a little pot tucked inside and have a spoon to eat with.