Preheat the oven at 180deg C.
Prepare a baking tin by lining and dusting .
Peel and mash the bananas .
Add sugar , oil and vanilla extract .
Mix well using a blender .
Sieve the flour , baking powder , baking soda and salt .
Gradually add the dry ingredients to the wet , mixing well .
Add the chopped walnuts and mix again .
Pour into the cake tin and bake at 180 deg C for 40-45 minutes or until a skewer comes out clean .