Preheat oven to 350 degrees. Spray a loaf pan with cooking spray and set aside.
Combine the flours, baking soda, and salt together in a small bowl.
In a separate bowl, beat the sugars and oil with a mixer until creamy and smooth. Add the mashed banana, eggs, buttermilk, and vanilla then beat until blended. Gently fold the flour mixture into the banana mixture and mix batter until just combined.
Place chocolate chips in a medium microwave-safe bowl and microwave for 30-40 seconds or until almost melted. Stir until smooth (cook for a few more seconds if it's not completely melted).
Add 1 cup batter to the chocolate, stirring until well combined. Spoon batter into prepared loaf pan, alternating between plain batter and chocolate batter. Swirl batters together using a knife. Place additional chocolate chips on top, if desired.
Bake for 70 minutes, or until a tester inserted in the center comes out clean. Cool 10 minutes in the pan before removing from pan to wire rack to cool completely. Slice and serve. Enjoy.