For the cake, place all of the cake ingredients into a food processor and blend briefly until well combined - don't overmix.
Grease a 600ml/1 pint pudding basin with softened butter. Spoon the mixture into the basin and smooth the top with a wet palette knife.
Cover with cling film and microwave on high for 6-7 minutes, or until well risen and springy to the touch.
Leave to cool, then loosen the edges and turn out onto a plate.
For the icing, mix the yoghurt, icing sugar and orange zest together in a bowl.
To serve, drizzle the icing over the cake and garnish with mint.
