1. Preheat your oven to 350F (176C) and prepare a muffin pan by spraying the cavities with cooking spray or lining them with paper liners. Set aside.
2. In a large mixing bowl, combine the flour, oats, baking powder, baking soda, cinnamon, and salt. Set aside.
3. Lightly beat the egg in a separate bowl. Whisk in the yogurt, applesauce, brown sugar, vanilla, and grated apple, stirring until well-combined.
4. Add the wet ingredients to the dry ingredients, mixing gently until just combined. Fold in the raisins.
5. Divide the batter evenly among the 12 muffin cups, filling them almost to the top. Add a sprinkle of oats if desired.
6. Bake the muffins for 20-22 minutes, or until top is firm to the touch and toothpick inserted into the centre comes out clean. Allow the muffins to cool in pan for ~10 minutes before transferring to a wire rack to cool completely. Store them in an air-tight container for up to 5 days, or freeze them for up to 3 months.