Combine flour, brown sugar and throw in your diced apple to coat the pieces. Then mix in the oats, walnuts, baking soda.
In a separate bowl mix together melted butter, apple sauce, egg, cinnamon and peanut butter.
Stir the wet peanut butter mixture into the dry ingredients until combined. Spread mixture into lightly greased 9 x 13 baking pan. Bake for 20-25 minutes, until lightly browned. Remove from oven and cool before cutting into bars.