Preheat the oven to 375 degrees F. Line two muffin tins with 18 liners. Set aside.
In a medium-sized bowl, whisk together the flour, cocoa powder, baking powder, cinnamon, and salt. Set aside.
In a microwave-safe bowl, microwave the dark chocolate in 30 second increments. Stir in between each interval, and microwave until melted. Set aside and allow to cool slightly.
Scoop insides of avocados, discarding the pits, into the bowl of a stand mixer. On low speed, beat until smooth. Add the buttermilk, sugar, vanilla extract, egg, and vegetable oil. Beat again until smooth.
Little by little, add the flour mixture to the wet ingredients. Mix until just combined.
Drop the muffin batter into the prepared liners, filling them approximately 3/4 of the way full. Top with semi-sweet chocolate chips (the more, the better).
Bake for 20-25 minutes, or until a toothpick, when inserted into the center, comes out clean. Allow them to cool in the pan for 5 minutes or so before removing them to a wire rack to finish cooling completely.