Preheat oven to 375F. Line a muffin tin with muffin liners, then give them a quick squirt of non-stick spray.
Combine all dry ingredients (oats, flour, sugar, BP, BS, salt, & cinnamon) in a mixing bowl, whisking until well combined.
In a separate bowl, mash bananas with the back of a fork.
Add egg (or flax egg), butter (or oil), and extracts to the bowl with the banana.
Stir the dry ingredients into the wet until no pockets of flour remain.
Fold in the blueberries.
Scoop batter into prepared muffin tin, filling each about ⅔ of the way full.
Make the oat topping by mixing all the ingredients together in a bowl.
Divvy the topping evenly over the muffins.
Bake in a preheated oven for 18-22 minutes, or until a toothpick comes out clean.