To a medium-size bowl, add all-purpose flour, baking powder, ground cinnamon, and a pinch of sea salt. Mix with a whisk and set aside.
Add bananas to a large bowl and mash them well with a potato masher or fork into applesauce-like consistency. Add maple syrup, sunflower oil, unsweetened almond milk, and apple cider vinegar, and stir to combine.
Sift the flour mixture into the mashed banana mixture and mix everything with a spatula until incorporated. Finally, fold in chopped walnuts.
Heat the waffle iron and spray it with oil (if you don’t have non-stick waffle iron). When your waffle iron is hot enough, pour the batter (1/2 batter for 2 waffles) to cover the waffle iron on each side. Cook until golden brown, about 7-10 minutes. Remove from iron, set aside, and repeat the process with the remaining batter. Serve warm with sliced banana and maple syrup.