Preheat the oven to 350F (180C or 170C fan forced).
Line the bottom of two 9-inch cake pans (see recipe notes for pan alternatives) with rounds of parchment paper. Lightly grease the sides of the pans.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon and salt. Set aside.
In a very large bowl, beat together the butter, granulated sugar and brown sugar until there are no lumps of brown sugar or butter (about 1 minute). Then beat in the oil.
Add in the vanilla extract and beat in the eggs 1 at a time, turning off the mixer and scraping down the sides and bottom of the bowl as you go.
Turn off the mixer and whisk in the mashed bananas.
With the mixer on a low speed, beat in about ⅓ of the dry ingredients.
Scrape down the sides and bottom of the bowl. Then beat in about ½ of the milk.
Turn off the mixer. Whisk in about ⅓ more of the dry ingredients followed by the rest of the milk.
Then whisk in the rest of the dry ingredients. You will see some lumps in the batter from the banana - that is expected and OK.
Gently fold in the chocolate chips with a rubber spatula or wooden spoon.
Divide the batter evenly between the two prepared pans.
Bake both on the same rack of the oven in the middle for about 35-40 minutes, or until an inserted toothpick comes out with a few crumbs. I typically don't say clean with this recipe, as sometimes the toothpick can come out clean but the middle of the cake is still gummy.
Cool the cake layers in the pans for about 20 minutes, then carefully invert and continue cooling on a wire rack.