Preheat oven to 350 degrees. Line a 9x5 loaf pan with parchment paper.
Mash bananas in a bowl with fork or potato masher. Add maple syrup, coconut sugar, vanilla extract and almond coconut milk. Mix well.
In a separate bowl, combine oat flour, arrowroot starch, sea salt, baking powder, and baking soda. Add wet ingredients and stir gently, until ingredients form a batter. Add frozen blueberries and fold in very gently, stirring just until mixed in.
Pour batter into loaf pan. Top with walnuts, if desired, and bake in oven for 40 minutes. Then turn off oven and leave blueberry banana bread in oven for another 10 minutes. Remove from oven and cool completely, on a rack, before slicing. Serves 4.