Add the olive oil, eggs, maple syrup, vanilla and apple cider vinegar to a large mixing bowl and using a hand blender, blend for about 30 seconds, till well combined.
In a small mixing bowl, whisk together coconut flour, almond flour, cocoa powder, baking soda and salt.
Pour the dry ingredients into the wet ingredients and whisk until well combined, batter will be very thick.
In small mixing bowl (that was previously used for dry ingredients) combine ripe bananas and milk and blend together, using a fork. Mixture will be lumpy.
Pour banana mixture into batter and whisk till well combined. Fold in chopped dark chocolate bar and walnuts.
Spray a glass loaf pan with cooking spray (or coat with coconut oil or butter). Cut a piece of parchment paper to lay in pan so that it covers the bottom and goes up both long sides of the pan.
Pour batter into loaf pan and bake at 350 degrees for 55 minutes, till bread is cooked through and toothpick comes out clean.
Let cool in pan for about 30 minutes and then remove from pan and let finish cooling on wire rack.
Once cooled, slice and serve!