I cook nearly all my sweets with buckwheat flour. Contrary to its name, buckwheat is not related to wheat. It is actually not even a grain, it’s a seed; a fruit seed specifically (part of the rhubarb family). It is also gluten free and nutrient-dense; a veritable super-food, jam packed full of flavonoids, minerals and protein (1 & 2).
I find the bananas, vanilla essence and cinnamon all have a natural sweetness so I only use a quarter of a cup of coconut sugar. If you like your muffins sweeter, increase the coconut sugar to half a cup, or even a little more.