Preheat the oven to 350 degrees. Line a muffin tin with muffin liners. In a small bowl, whisk together flax seed meal and water. Set aside for 5 minutes. Combine non-dairy milk and apple cider vinegar in a bowl and let sit for 5 minutes.

To a large mixing bowl, mash bananas until smooth and nearly no lumps remain (a little is fine). Add flax mixture, milk, applesauce, vanilla extract, and coconut sugar. Whisk until smooth. Add flours, baking soda and powder, and salt. Use a wooden spoon or spatula to combine until a thick, but pourable batter forms. Fold in walnuts.

Use a cookie scoop to evenly distribute batter into muffin liners. They should be nearly full which is fine. Bake for 25 minutes until a toothpick inserted comes out clean and tops are golden brown. Let cool for 5 minutes in the muffin tin before transferring to a wire cooling rack.