Preheat oven to 375ºF/190ºC and line a mini muffin tin with 24 liners.
Set a sieve over the bowl of your stand mixer (or a big mixing bowl) and sift together the flour, baking powder, baking soda, salt, and cocoa powder. Stir in the oats.
Fit the stand mixer with the paddle attachment. Add brown sugar to the dry ingredients and mix on low speed for about 30 seconds.
Melt the room temperature butter in a glass measuring cup in the microwave. Mash the bananas in. Stir in the yogurt and egg and mix well. Add a splash of vanilla.
With the mixer running on low, pour the wet mixture into the dry mixture. Increase the speed to medium and stir until everything is just incorporated, being careful not to over-mix. Fold in the semi sweet chocolate chips using a rubber spatula.
Divide the batter into the mini muffin cups (about a tablespoon/muffin). Bake for 15 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Cool on a cooling rack before enjoying!
Notes
Feel free to use white whole wheat flour or all purpose flour if you would like.You can use any oil like vegetable or coconut oil instead of butter.I used semi sweet mini chocolate chips. Feel free to use dark or sweet ones. If you want your muffins to be more chocolaty you can increase the quantity of chocolate chips a little bit.