Heat oven to 425F. Grease a 12 well muffin tin and set aside.
In a food processor or blender, pulse the oats until they are partially chopped. They should be mostly oat pieces (not flour) with few whole oats left.
Pour the milk into a 2 cup container. Add the oats and let them soak for 20-30 minutes.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
In a large bowl whisk together the oil, sugar, egg, vanilla, and bananas.
Add the dry ingredients to the wet along with 1/2 cup of the chocolate and mix lightly but completely.
Divide the batter evenly into the prepared muffin tin. The batter will be quite wet.
Top each muffin with some of the remaining chopped chocolate.
Bake 5 minutes.
Reduce heat to 350F. Bake 15-18 minutes more, or until a toothpick comes out with only a few moist crumbs.
Cool for 10 minutes in the tin. Then turn out the muffins onto a cooling rack and let cool to room temperature.