Preheat the oven to 350°F. Spray an 8x4-inch loaf pan with cooking spray and line the bottom with parchment paper.
In a large mixing bowl, mash the bananas with a fork until smooth. Add the sugar, oil, eggs, and vanilla. Whisk until fully combined.
In a separate bowl, whisk together the flour, cocoa powder, baking soda, and salt.
Add the dry mixture to the wet ingredients and stir until just combined. Do not overmix.
Toss 1 cup of chocolate chips with 1 tablespoon flour, then fold them into the batter.
Pour the batter into the prepared loaf pan. Sprinkle the remaining ¼ cup chocolate chips over the top.
Bake for 55–65 minutes, or until a toothpick inserted in the center comes out mostly clean (a few moist crumbs are fine).
Let the bread cool in the pan before removing and slicing.