Pre-heat oven to 160oC and line a muffin tin with muffin cases.
In a bowl cream together the butter and the Greek yoghurt.
In the same bowl add the mashed banana and mix well.
Add the eggs one at a time into the mixture along with the vanilla and whisk together.
Over the mixture sieve in the wholemeal flour, ground oat flour, baking powder, bicarbonate of soda and cinnamon. Mix well so all the ingredients are combined but take care to not over mix.
Add the chopped apple and blueberries into the batter and stir evenly into the mixture.
Spoon the mixture into the muffin cases until they are 3/4 full. Sprinkle 1/2 tsp oats over the top of each muffin.
Place in the oven on the middle shelf and bake for 20-25 minutes. Do not open the door before this as it stops them rising.
Test with a skewer, it should come out clean.
Once baked, leave in the tray for 10 minutes before transferring to a wire rack to cool.
Store in an air-tight container, in the fridge, for up to 3 days.