Preheat oven to 350°F and grease the pan of choice with cooking spray or baking spray. You can also line the pan (unless a bundt) pan with parchment paper for easy removal. See notes for pan size options.
In a large mixing bowl, whisk together the oil, sugar, eggs, vanilla extract and mashed bananas.
In a separate bowl, whisk together the baking soda, baking powder and gluten free flour.
Alternate adding the flour mixture and oat milk to the liquid mixture, beginning and ending with the flour. Mix in between each addition until just combined. Once all the ingredients are added, mix well until no lumps remain.
Using a rubber spatula or spoon, fold in the chocolate chunks.
Pour the batter into the prepared pan(s) and bake! Fill pans ¾ of the way. Standard loaf cakes should cook about 1 hour 20 minutes. If using a different pan size, check at the 45 minute mark and bake until a toothpick inserted into the center comes out clean. Cupcakes will cook shorter though, about 25-28 minutes.
Allow to cool about 20 minutes before flipping the cake out of the pan to finish cooling. Store in a ziplock on the counter.