Preheat oven to 180 degrees and grease a large loaf pan well.
Whisk ingredients from flours to coconut in bowl well till combined.
In a jug, whisk the mashed bananas, coconut oil and buttermilk well and pour over the dry ingredients. Fold in till combined.
Pour into the prepared pan and bake for 60 to 70 minutes, till the skewer comes out clean.
Cool in the pan for 10 minutes, before flipping onto a wire rack to cool completely.