Preheat oven to 325°F. Grease a 13×9 inch baking pan and set aside.
In a large bowl, mix together vegetable oil and sugar. Stir in eggs, one at a time. Add in bananas and vanilla and stir to combine.
In another bowl, stir together flour, baking powder, baking soda and salt.
Working in batches, stir ⅓ of the flour mixture into the sugar mixture. Add ⅓ of the milk and stir. Repeat until everything is mixed together. Stir in chocolate chips.
Pour batter into baking pan and spread out evenly. Bake for 35 minutes or until a toothpick comes out of the centre clean.
Let cake cool in the pan on a rack for 10 minutes before attempting to remove from the pan.
Before serving, sift powdered sugar and cocoa powder on top, if desired.