Preheat oven to 180C (350F) and line a loaf tin with baking parchment (greaseproof paper).
Crush the walnuts (Optional: keeping back 8 halves to decorate the top) into smaller chunks and toast in a dry frying pan over a low heat until they start to brown (about 5 mins).
Mash the bananas in a mixing bowl and add the almond flour (ground almonds), eggs, coconut oil and maple syrup. Mix well.
Add the toasted walnuts and bicarbonate of soda and mix well to make sure everything is evenly distributed.
Pour the maple walnut banana bread mixture into the loaf tin and top with the walnut halves.
Bake in the oven for 40-45 mins or until a skewer inserted comes out clean. If the top starts to brown before the cake is ready, cover with a piece of tin-foil to prevent it getting too brown.