Pre-heat the oven to 400 degrees.
Pour 1 cup of old fashioned oats into a blender. Process about 30 seconds until the oats are ground into a fine powder. Set aside.
To a medium-sized bowl, mash the brown/black bananas. Add the brown sugar, eggs, melted butter and vanilla extract. Stir together to combine. Add the sourdough discard and stir until combined.
To a small bowl, whisk together the ground oats, flour, cocoa powder, salt and baking powder. Add this dry mixture to the wet banana mixture. Stir until just combined. You should still see some streaks of flour throughout the batter.
Add the 1/2 cup of chocolate chips and gently stir again until just incorporated. Over-mixing the batter can result in rubbery muffins. We are looking for light and tender muffins, so stir until just combined.
Lightly grease a 12 cup muffin pan. If using muffin liners, spray the muffin liners as well. Using a cookie scoop or 1/4 cup measuring cup, fill each muffin tin 3/4 of the way full.
Bake the muffins for 5 minutes at 400 degrees. After 5 minutes reduce the temperature to 325 degrees and bake for 15 more minutes.
Let muffins cool in the pan for about 5 minutes and then turn out and place on a cooling rack. Enjoy!