Preheat the oven to 360° F (180° C). Prepare a loaf tin and cover it with baking parchment.

In a large mixing bowl, combine the flour, baking powder, cinnamon, cocoa powder, chopped walnuts, and a pinch of salt.

In another bowl, mash 3 of the bananas until smooth, and combine with the maple syrup, melted coconut oil, vanilla essence and 2 eggs. Add a pinch of salt, and whisk together until the wet ingredients are smooth.

Pour the wet mixture over the dry ingredients, and stir with a spatula to combine.

Pour the mixture into the prepared loaf tin, smoothing it out to make sure the batter is even. Slice the remaining banana in half and place flat-side-up in the top of the loaf, pressing down gently.

Place the tin in the middle of the oven and bake for 50-60 minutes, until a toothpick comes out clean. Cover with foil after 30 minutes to avoid the top over-browning.

Remove from the oven and let it rest for 15 minutes before placing on a wire rack to cool fully before slicing.

Store the bread at room temperature for up to 4 days or in the freezer for up to 3 months. Ensure the bread is fully cooled before freezing.