Preheat oven to 350°F. Prep/line a 9 x 5 loaf pan.
In a medium bowl, whisk together flour, cocoa powder, baking soda, and salt. Set aside.
In a large bowl, mash bananas until smooth. Stir in sugar, oil, and vanilla.
Stir dry ingredients into banana mixture until just combined. If using, fold in chocolate chips.
Fill loaf pan and bake on 350°F for 60 minutes, or until top springs back when touched and/or a toothpick inserted comes out clean.
Rest in pan for 5 minutes. Remove from pan and let cool for an hour for easier cutting. Store covered at room temperature for up to 3 days.