Preheat oven to 350°F and line a 9×5″ bread pan with parchment paper or lightly coat it with oil. Mix the flaxseed meal with the water and stir well. Set aside to thicken, about 15 minutes.
n a large bowl, add the oat flour, baking soda, baking powder, salt, cinnamon, and nuts if using. Mix well until uniform and set aside.
In a food processor, add the dates, almond milk, vanilla extract, and apple cider vinegar. Process until smooth, and then mix in the mashed banana and flax egg with a spoon until combined. Add the date and banana mixture to the dry mixture and stir until a batter forms.
Pour the batter into the prepared loaf pan and if desired top with the optional banana, cut side facing up (refer to photos in post).
Place into the oven and bake for 50-60 minutes, or until a toothpick runs clean. Remove from the oven and cool completely before cutting.*