Preheat oven to 350 degrees Fahrenheit.
Grease a 6-inch pan with coconut oil. Zest one of the oranges and set aside to be used in cake batter. Then peel the oranges carefully and slice into rounds. Arrange the orange rounds to cover the entire bottom of the pan in a flat layer. You can pull apart one ring to fill the empty spaces with smaller orange wedges. Reserve any unused orange pieces for the juice for the cake batter.
To make the cake batter, in a large bowl combine all of the dry ingredients and mix well until thoroughly combined. Then add the wet ingredients, and mix well until completely incorporated.
Pour on top of the orange slices. It will be a little thick, so use a spatula to press it down and make sure it reaches the edges of the pan.
Bake for 30-32 minutes, until a toothpick comes out clean. Let cool before removing from pan. Flip it over right onto your serving tray.