Preheat oven to 400 degrees Fahrenheit. Line a 12-cup muffin tin with paper liners and set aside.
In a large mixing bowl, mash the bananas.
Beat in the oil and eggs, then add the brown sugar and mix until well-blended.
In another large bowl, mix together the flour, cocoa powder, and baking soda.
Pour the dry ingredients into the wet and stir until just combined.
Stir in the chocolate chips.
Using a large cookie scoop, portion out the batter filling the cups about 1/3, then place a scoop of peanut butter (about a teaspoon or two) into the center of each muffin. Cover with more batter until each cup is 3/4 full.
Bake for 15-20 minutes, or until the tops spring back when lightly pressed.
Leave in pan for 5 minutes, then turn onto wire racks to cool completely.