Use a vegetable slicer or a potato peeler to make courgette ribbons, then grill them. Grate the orange and lime zest and add to Robiola Osella. To make the filling softer, you can add a few drops of juice. Roughly chop the pistachios and add them to Robiola Osella. Mix all the ingredients evenly together. Spread a thick layer of Robiola Osella onto the grilled courgettes and roll them up. When all the rolls have been made, stand them on end like little towers and place the prawns on the top.