Preheat the oven to 375°F and spray a muffin pan with baking spray.
In a medium bowl, add the oat bran, rolled oats, and buttermilk. Stir to combine and let the mixture soak for 10 minutes. Meanwhile, prepare the other ingredients.
In a large bowl, add the butter, egg, sugar, banana, and vanilla. If the banana is not mashed yet, use a potato masher or a fork to smush it up. Stir the mixture until well combined.
In a separate bowl, whisk together the flours, baking soda, baking powder, salt, and spices. Add to the wet ingredients and gently stir until just nearly combined.
Add the chocolate chips and gently stir until combined and evenly distributed.
Divide the batter equally among the 12 spaces in the muffin pan. Bake for 15- 18 minutes. Cool in the pan for 10 minutes before removing them to a cooling rack.
Notes
Other additions could be nuts, crystallized ginger, or even shredded coconut!