Heat the oven to 180 C (356F).
Grease a large sponge cake/sweet bread pan with some olive oil.
In a medium bowl, mix the flour, baking powder and salt; put aside.
In a large bowl, mix the sugar, oil, eggs and vanilla extract, using an electric hand mixer.
Add the mashed bananas and mix to incorporate the ingredients.
Add the flour mixture to the wet ingredients and mix until completely homogenized.
Using a rubber spatula, add and incorporate the walnuts.
Pour the batter in the pan.
Bake for approx. 45 minutes or until it passes the toothpick test.
Let the cake cool for 10 minutes in the pan, then transfer it to a cooling rack. Slice only when it is completely cool.