Preheat the oven to 375F (190C). Grease a 9x5-inch loaf pan with cooking spray or vegan butter and line with parchment paper for easy removal.
In a large bowl, whisk together gluten-free flour blend, xanthan gum (if using), baking powder, baking soda, cinnamon and salt.
In a separate bowl, mash the bananas.
Then, mix the bananas with the brown sugar, vegetable oil, unsweetened applesauce, apple cider vinegar, and pure vanilla extract.
Pour the dry ingredients into the wet ingredients and mix until just combined.
Fold the chocolate chunks into the batter.
Then, pour the bread batter into the prepared pan. Sprinkle the top with turbinado sugar or extra chocolate chunks if you’d like.
Bake at 375F for 55-70 minutes, until the bread is lightly browned and a toothpick inserted in the center of the bread comes out clean. If the bread is browning too much, cover the loaf pan with aluminum foil and continue baking.
Cool in the pan for 15 minutes before transferring to a wire rack to finish cooling.