Preheat the oven to 175 C.
In a large bowl, combine plain yoghurt, mashed banana, honey and baking soda.
In a separate bowl, combine all purpose flour, oat flour, chopped walnuts, cinnamon and salt.
Pour the dry ingredients into the bowl with the wet ingredients and use a spatula to combine.
Batter a small square bread loaf (13 cm x 13 cm).
Transfer the batter into the buttered bread loaf and press down gently.
Bake in the middle of the oven for about 50 min.
Cover the loaf with aluminium foil and bake for another 40 min. The internal temperature of the bread should now be at least 99 C.
Remove bread from the oven and let cool in the loaf for at least 1.5 hours.
Slice and enjoy!