Preheat oven to 350 degrees. Grease a 8 ½ x 4 ½ inch loaf pan.
Using a hand mixer cream butter, sugar and peanut butter in a bowl. Add eggs one at a time and mix.
In a separate bowl whisk together the flour, cocoa powder, baking soda, salt and cinnamon. Add the mashed banana to the creamed sugar and beat until incorporated. Add the dry ingredients and mix until just combined. Stir in half the chocolate chips by hand and pour the batter in the loaf pan. Sprinkle the remaining chocolate chips on top.
Bake for 45-50 minutes until a toothpick inserted into the cake comes out clean. Once cooled, remove banana bread from loaf pan. Drizzle with melted peanut butter. Slice and serve.