Preheat oven to 400ºF and line a muffin tin with 12 liners.
In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cocoa powder.
Beat the egg in a large bowl. Stir in the oats, banana, yogurt, sugar, and coconut oil and mix well.
Pour the dry mixture into the wet mixture. Stir until everything is just incorporated, being careful not to over-mix. Fold in the chopped dark chocolate.
Divide the batter into the muffin cups. Bake for 17–20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Notes
If desired, top your muffins with thinly sliced bananas, additional oats, chocolate chips, or a sprinkling of turbinado sugar before baking.