Preheat oven to 350 F.
Mix ground flax seed and water in a small mixing bowl. Set aside for five minutes.
Add banana to mixing bowl and mash until smooth. Add flax egg, coconut flour, baking soda, and salt. Stir in walnuts.
Bake at 350 F for 25-30 minutes until cooked through.
Top with coconut or Greek yogurt, more walnuts, chocolate chips, or maple syrup! Enjoy!