Preheat the oven to 160°C on fan-force (320°F) and grease and line a 24x14cm loaf pan.
Use a fork to mash the bananas, coconut sugar and vanilla into a small mixing bowl until well combined.
Sift all the dry ingredients into a larger mixing bowl and use a balloon whisk to stir until well combined.
Make a well in the middle of the dry ingredients, then add the melted coconut oil and banana mixture and whisk until just combined.
Pour batter (it should be quite thick) into the prepared loaf pan and bake on the middle rack for 55 minutes, or until a skewer inserted in the centre comes out clean.
Combine all ingredients into a blender and blend until extremely smooth (the time this takes will depend on the quality of your blender, should be anywhere from 1-3 minutes). If necessary you can add a tablespoon of warm water to assist your blender in making it smooth.
Spread the frosting over the cake once it has completely cooled and dust with cinnamon to finish (if you like). Keep stored in the fridge for up to 5 days, but best enjoyed served at room temperature.
*You can sub this 1/2 cup of packed organic brown sugar instead for a more traditional tasting banana cake, but I prefer coconut sugar for sustainability and health reasons :)