Preheat the oven to 350 degrees F (177 degrees C). Spray 12 muffin tins with non-stick spray or line them with muffin liners.
In a small bowl, mix the ground flax and water together to create a flax egg. Set it aside so that the mixture can thicken.
In a medium bowl, mix the soy milk with apple cider vinegar. Set it aside to allow the milk to curdle a bit, just like homemade buttermilk.
In a large bowl, mix the flour, sugar, baking powder, baking soda, and salt together. Add the milk, maple syrup, vanilla extract and mashed bananas until well incorporated. Fold in the coconut and chopped walnuts.
Pour the muffin batter into the 12 tins. I was able to fill them all to the top.
Bake the muffins for about 15 to 17 minutes, or until a toothpick comes out clean. Let the muffins cool for a few minutes before eating.
Store the muffins in an airtight container in room temperature for a few days or refrigerate them.