Preheat oven to 350 degrees. Line a 12 cup muffin pan with liners or spray with nonstick cooking spray, set aside.
In a large mixing bowl, whisk together the bananas, sugar, oil egg, and vanilla. Add in the flour, oats, cinnamon, baking soda, and salt and stir to combine. Use a muffin scoop to distribute the batter between the muffin cups.
To make the topping, stir together the sugar and cinnamon. Sprinkle overtop of the muffins. Bake for 18-22 minutes, or until a toothpick inserted in the muffin comes out clean. Let cool on a wire rack.
Notes
Make ahead! These muffins do great stored in an airtight container in the refrigerator or freezer. Whip up a batch and have a delicious and healthy treat anytime.