In a large bowl, ombine the flours, oats, baking powder, baking soda, cinnamon, and salt. In a separate bowl, whisk buttermilk, applesauce, maple syrup, vegetable oil, egg and vanilla until well blended. Add the wet ingredients to the dry ingredients and stir just to incorporate (do not overmix). Fold in chopped apples and nuts, if using. Divide batter equally among muffin cups (batter will reach top of cups). Bake until muffin tops are golden brown and tester inserted into center of muffins comes out clean, about 25-28 minutes. Transfer to rack and allow to cool.