Line an 8" x 4" Loaf pan with parchment paper and Preheat the oven at 350°F (325°F if using convection oven).
Sift almond flour and combine with coconut flour, ground flax seeds, protein powder, cinnamon, salt and baking powder. Set aside.
Mash 2 of the 3 bananas.
Slice the third banana lengthwise and chop walnuts. Set aside.
Mix the softened butter with the mash banana using a whisk, hand beater or stand mixer.
Continue to mix while adding one egg at a time.
Once all eggs are incorporated, add the mix of flours and mix well.
Add the chopped walnuts to the batter and mix well.
Pour batter into baking pan and place in the oven.
Bake for about 40 minutes. Use a toothpick or a small knife and insert it into the center of bread. When you pull it out, it should come away clean.