Preheat oven to 350 degrees. Line or grease a muffin tin, set aside.
In a large mixing bowl, combine the sugar and oil, whisk well to combine. Add in the milk, eggs, and vanilla and whisk again until smooth. Fold in the mashed bananas.
In a separate mixing bowl combine the flour, cocoa powder, salt, baking soda, and cinnamon, stir to mix. Add the dry ingredients into the wet ingredients, mix until smooth. Fold in the chocolate chunks, if desired set a few aside to top the muffins with. Using a measuring spoon or a portion scoop, scoop batter into the prepared muffin tin, filling each one ? of the way full. Top with reserved chocolate chunks if desired.
Bake at 350 degrees F, for 20-25 minutes, or until a toothpick inserted comes out clean. Transfer to a wire rack to cool and enjoy.