Preheat oven to 375F. Grease a 9 x 5-inch bread pan with cooking spray or vegan butter.
In a large bowl, whisk together gluten-free flour blend, xanthan gum (if using), salt, baking soda, and baking powder.
In a separate bowl, mash the bananas.
Then, mix the bananas with the granulated sugar, vegetable oil, apple cider vinegar, and pure vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Toss the blueberries with 1/2 tablespoon of gluten-free flour until they are coated.
Carefully fold in the blueberries to the batter.
Then, pour the bread batter into the prepared pan. Sprinkle with turbinado sugar if you'd like.
Bake at 375F for 60-70 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.