Place oats in a small bowl, pour in buttermilk.
Leave the mixture for an hour or two at room temperature.
Preheat oven to 190 degrees C. Grease 12 muffin cups or line with paper muffin liners.
In a large bowl, stir together whole wheat flour, baking powder, baking soda and brown sugar.
Stir in oat/buttermilk mixture, applesauce and egg; mix well. Pour batter into prepared muffin cups.
Sprinkle the top with cinnamon and brown sugar. Bake in preheated oven for 30 minutes.