Preheat oven to 200 degrees C. Grease 12 muffin tin or line with paper muffin liners.
Muffin: In a medium bowl whisk together oats, flour, baking powder, bicarbonate of soda and cinnamon; set aside.
In a large bowl whisk brown sugar, egg white, apples and milk until smooth. Stir in the flour mixture until evenly moistened; it's ok if small, dry lumps remain. Pour the mixture into the prepared muffin tin.
Topping: In a small bowl combine the oats, brown sugar, cinnamon and melted butter. Sprinkle mixture over the muffins.
Bake in the preheated oven for 20 minutes or until golden and the tops spring back when lightly pressed. Cool at least 10 minutes before serving.