For the banana bread: Preheat oven to 350 degrees. Line a 10x10 baking pan with parchment paper.
In a mixing bowl, use a potato masher to completely mash the bananas. Add coconut oil, honey, flax egg and almond butter; mix well. Add coconut flour, chia seeds, baking soda, nutmeg, peppermint leaf powder (optional), and vanilla extract, and mix until thoroughly combined.
Use a spatula to spoon mixture into the prepared baking pan. Bake for 30 minutes, then remove and let cool for 10 minutes.
For the mousse: In a medium bowl, use a potato masher to mash avocados, then transfer to a blender. Add remaining ingredients and blend until smooth.
For assembly: Use the rim of a wide-mouth Mason jar to cut banana bread into rounds. Layer banana bread with spoonfuls of mousse, soy whipped cream, walnuts and banana slices. Top with whipped cream, more banana slices and walnut pieces.