Preheat oven to 350 degrees F.
Line a loaf pan with tinfoil or parchment paper and spray with nonfat cooking spray.
Combine flours, baking powder, baking soda, salt in a large bowl.
In a medium sized bowl, beat butter and sugar until blended, then blend in eggs.
Add mashed banana, milk, chia seeds and vanilla and stir to combine. Add wet mixture to dry mixture and stir to combine.
Fold in ¾ cup dark chocolate chips and ¾ cup walnuts.
Pour into prepared loaf pan. Sprinkle remaining ¼ cup dark chocolate chips, ¼ cup walnuts overtop the batter, evenly.
Bake for 60-65 minutes, or until a toothpick inserted comes out clean. Baking time may vary, depending on oven. Remove from oven and let cool. Slice and serve.