Pre-heat oven to 350 and spray a 15 x 10 x 1 baking pan with cooking spray or place a Silpat Entremet silicone baking pan on a large baking sheet.

In a medium bowl, whisk together whole wheat pastry flour, oats, white flour, flax seed meal, baking powder and salt; set aside.

In a stand mixer, cream together coconut oil, brown sugar and white sugar over high speed until nice and creamy - about 2 minutes.

Reduce mixer speed to low and slowly add in yogurt and vanilla. Add eggs in one at a time and blend until incorporated.

Add mashed bananas and blend until combined using a rubber spatula to clean the sides of the bowl.

Slowly add the dry ingredients to the wet and blend until just incorporated - careful not to over mix.

Remove bowl from the stand mixer and gently fold in chocolate chips and chopped walnuts.

Pour mixture into baking pan and bake for 45 minutes until golden brown and toothpick comes out clean. Let cool completely before slicing into 24 bars.