Preheat oven to 350 F. Grease a 8 inch square or round pan with oil. Then line with parchment paper.
Pour a little bit of oil onto the parchment paper. Spread it evenly and then sprinkle an even layer of sugar.
Cut the peel off of the oranges and slice them against the segments. They should be around 1/2 a centimeter thick. Arrange them in the pan (on top of the sugar) to cover all the space. Overlap and cut pieces as needed.
In a large bowl, combine all the ingredients for the cake. Mix just to combine, do not over-mix!
Pour the batter on top of the arranged oranges and level it out. Create a shallow dip in the center so that when it's finished baking, the top is level to flip over.
Bake for 50-55 minutes or until golden brown and a toothpick inserted comes out completely clean. If you want to eat it warm, run a knife around the edges and flip the cake out on to a plate. Otherwise, let the cake cool completely and then flip it out.