Preheat the oven to 350ºF. Line a 12 cup muffin pan with paper liners or coat with cooking spray.
In a medium bowl whisk together banana, applesauce, canola oil, and egg.
In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Add the banana mixture to the flour mixture and stir just until all the flour is incorporated.
Fold in the chocolate chips and walnuts.
Divide batter evenly amongst prepared muffin cups. Bake 25 minutes or until a toothpick inserted into the center of one of the muffins comes out clean.