Pre-heat oven to 180°C/160°C fan/gas mark 4. Grease and line a 9 inch loaf tin.
Make the chia egg by mixing the ground chia seeds in a small bowl with the 3 tablespoons of water. Place in the fridge and it should be ready to use by the time you get to that step.
Mix the flours in a large bowl with the desiccated coconut, cocoa powder, bicarbonate of soda and salt and set aside.
Pour the coconut milk and apple cider in a food mixer and beat until it's frothy, do not overbeat in case the coconut milk should separate.
Add the bananas, sugar, coconut oil, vanilla and the chia egg into the coconut milk and beat together until smooth.
Spoon one third of the flour mixture in and mix until smooth, then the next third then mix, then the next*.
Pour the cake batter into the loaf tin and smooth the surface.
Bake for 1 hour or until an inserted cocktail stick comes out clean.
Turn the cake out onto a cooling rack and leave to cool before adding the glaze.