Preheat oven to 180C (160 fan). Grease and line base of a loaf pan.
In a stand mixer or with electric beaters on medium high mix for 10 minutes, or until tick and pale and the mixture forms a ribbon when beater is lifted.
Reduce speed to low and beat in the oil in a steady stream.
Mix in the vanilla and yoghurt by hand and then the walnuts.
Add the bananas.
Stir together the flour, salt, bicarb soda and cinnamon in a large bowl and pour wet mixture into the dry mixture folding gently and thoroughly.
Pour mixture into pan and bake for 1 1/4 hours or until a skewer comes out clean when tested.
Cool in pan briefly then turn out onto a wire rack to cool.