Mix flour with baking powder. Set aside 1 tablespoon of the oatmeal. Peel, core and dice the apples. Add the cinnamon and remaining oatmeal, brown sugar and the diced apples.
Mix egg, oil, yogurt and milk in a separate bowl. Add the flour, oatmeal and apple mix from the other bowl and mix everything together well. Use a spoon to pour the batter into muffin cups. Spread the remaining tablespoons of oatmeal on top. Bake in the oven for about 20 minutes until golden brown (if you use large muffin tins, bake for about 5-10 minutes longer).