Preheat oven to 375° F. Line a standard muffin pan with baking cups.
In a large mixing bowl, stir together oats, gluten free flour blend, baking powder, baking soda, salt, and cinnamon until combined.
In a small mixing bowl, combine egg, oil, and vanilla.
Add the wet ingredients to the dry ingredients and stir until combined.
Add the mashed bananas and stir until completely combined.
Transfer the batter to the prepared muffin pan.
Prepare the Topping:
In a small bowl, stir together the brown sugar and cinnamon.
Sprinkle the brown sugar and cinnamon mixture evenly over the muffins.
Bake for 20 minutes or until a wooden pick inserted in the middle of a muffin comes out clean.
Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
Notes
Check the ingredients of your gluten free flour blend for xanthan gum. If your flour blend doesn’t contain it, try adding ½ teaspoon to the recipe.
When adding the wet ingredients to the dry ingredients, be careful not to overmix the batter. Over mixing the batter can lead to muffins that are tough.
Remove the muffins from the pan to finish cooling on a wire rack. If you leave the muffins in the pan to cool, the bottoms of the muffins may become soggy.