Preheat oven to 180°C (350 F). Grease and line the base and sides of a 11 x 21cm ( 4 x 8 inch) loaf pan with baking paper, allowing the sides to overhang.
Place the flour, coconut, sugar and bicarbonate of soda in a large bowl and stir to combine. Make a well in the centre.
Whisk the banana, oil and buttermilk together in a jug. Pour into the well. Use a wooden spoon to gently stir until just combined (do not overmix). Spoon into the prepared pan and smooth the surface.
Bake in preheated oven for 1 hour or until a skewer inserted in the centre comes out clean. Remove from oven and set aside for 5 minutes before transferring to a wire rack to cool.