Preheat the oven to 350°F (175°C). Line a 9×5-inch loaf pan with parchment paper or lightly grease it.
Blend the rolled oats in a high-speed blender until a fine flour forms. Skip this step if using oat flour.
In a large bowl, mash the bananas until smooth.
Whisk in the eggs, avocado oil, maple syrup, vanilla extract, and apple cider vinegar until fully combined.
Add the oat flour, baking powder, baking soda, sea salt, and cinnamon. Stir until a thick batter forms.
Gently fold the blueberries into the batter.
Transfer the batter to the prepared loaf pan and top with extra blueberries if desired.
Cover loosely with aluminum foil and bake for 40 minutes.
Remove the foil and continue baking for 20–35 minutes, or until the Oatmeal Blueberry Banana Bread reaches an internal temperature of at least 190°F (88°C) or a toothpick inserted into the center comes out clean.
Cool in the pan for 30 minutes before transferring to a wire rack. Slice and enjoy