Preheat your oven to 350°F (175°C). Grease a muffin tin or line with paper liners.
In a large bowl, mix the mashed bananas, sugar, and vegetable oil until well combined.
Add the beaten eggs and vanilla extract to the banana mixture. Stir until smooth.
In another bowl, whisk together the gluten-free flour, baking powder, baking soda, and salt.
Gradually add the dry ingredients to the wet ingredients, mixing until just combined. Do not overmix.
Gently fold in the blueberries.
Divide the batter evenly among the muffin cups.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
Allow to cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.