First preheat the oven to 350˚F or 175˚C and grease a standard 1-pound loaf pan with vegan butter or cooking spray.
In a large mixing bowl, mash the peeled bananas with a fork or potato masher then whisk the mashed bananas to smooth out larger chunks.
To the mashed banana, add the sugar, non-dairy milk, oil, vanilla and nutmeg and whisk until evenly combined.
Add the flours, tapioca starch, flax meal, baking soda, baking powder and salt to the wet mixture and whisk to remove any lumps of flour, being careful not to over-mix the batter. Once most of the dry ingredients are incorporated switch to a rubber spatula to finish mixing the banana bread batter.
If adding any mix-ins, fold them into the batter with a rubber spatula.
Pour the batter into the prepared loaf pan and smooth out the top with a rubber spatula.
Optionally sprinkle the top of the batter with cinnamon sugar to create a sweet crunchy top crust. Mix the cinnamon and sugar together in a small dish before adding it.
Bake the banana loaf cake in the middle of the center rack for 55-60 minutes or until it is nicely risen with a domed top and a dark golden brown color and a cake tester inserted in the center of the loaf comes out clean with a few moist crumbs.
Transfer the loaf pan to a cooling rack and let the loaf cake cool in the pan for 10 minutes. Run a dinner knife along the edged of the pan then tip the loaf out of the pan and let it cool completely to room temperature on the wire rack before slicing into it.