Peel the oranges and cut into bite-sized pieces (e.g. as the fillets run, cut eighths and then quarter the wedges again).
Put the yoghurt in a larger bowl, add the cinnamon while stirring constantly (ideally from a small shaker so that there are no lumps). Then add the vanilla sugar to the yoghurt and stir too. Finally add the oranges.
Note: You may or may not have to add vanilla sugar if the oranges are very sweet. If you don`t want to do without vanilla in this case, you can of course add some vanilla pulp if you like.