Preheat oven to 180°C. line and grease a 900g loaf tin.
Peel the bananas and mash with a fork then add to a bowl with the brown sugar, vanilla and oil then mix well.
In a separate bowl, combine flour, cinnamon and baking powder. Pour into the banana mixture and mix well to combine. Fold in the walnuts.
Transfer to the loaf tin and put into the oven to bake for 40 minutes. If the bread begins to burn or over darken, remove from oven and cover with foil before continuing to bake.