Heat the oven to 350ºF. Grease a 12-cup muffin tin and set aside.
Combine the flax and water and set aside to gel while you prepare the remaining ingredients.
In a small bowl, beat together banana, applesauce, yogurt and syrup (add vanilla extract also, if using). Whisk in flax egg and set aside.
Whisk together the dry ingredients in a separate bowl. Add to the wet and then stir to thoroughly combine (the batter will be kind of thick, but still stirable and soft).
Fill each cup ¾ of the way full. Add water to the ones that are unused. Sprinkle the tops of the muffins with quinoa flakes (and turbinado sugar) if desired. Let rest for 5 minutes before baking.
Bake on the center rack for 24 – 26 minutes until a cake tester inserted into the center comes out clean.
Cool in the pan for 5 minutes, then transfer to a wire rack and cool completely. Resist the urge to not break into them; cooling them will allow everything to set properly. If desired, reheat in the toaster oven or in the microwave.