Preheat oven to 375°F (190°C). Grease a 9 x 5-inch bread pan with cooking spray or vegan butter.
In a large bowl, whisk together 2 cups gluten-free flour blend, 2 teaspoons baking powder, 1 teaspoon baking soda, 1 teaspoon ground cinnamon, and 1 teaspoon salt.
In a separate bowl, mash the 4 very ripe bananas.
Then, mix the bananas with the ¾ cup granulated sugar, ⅓ cup vegetable oil, 1 tablespoon apple cider vinegar, and 2 teaspoons pure vanilla extract.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Toss the 1 cup blueberries with ½ tablespoon gluten-free flour blend until they are coated.
Carefully fold in the blueberries to the batter.
Then, pour the bread batter into the prepared pan. Sprinkle with 1 teaspoon turbinado sugar if you'd like.
Bake at 375°F (190°C) 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.