Wash the rhubarb and cut into pieces. Wash the untreated orange with hot water, dab dry, peel some of the peel thinly and cut into fine strips. Squeeze all oranges. Boil up rhubarb, orange juice, vanilla sugar and sugar together.
Mix the pudding powder with some water and pour it into the boiling orange juice. Bring to the boil again while stirring. Remove the groats from the stove and let them cool down a little. Arrange on plates and put half a cup of vanilla yoghurt on each of the rhubarb orange groats.
Sprinkle with orange peel.