Preheat oven to 425°F and grease a muffin tin or line with liners.
In a large bowl, mash bananas.
Add the eggs, vanilla, melted butter, and both sugars. Whisk to combine.
Add in the flour, oats, baking powder, baking soda, salt and cinnamon. Fold gently with a rubber spatula or a wooden spoon to combine.
Distribute batter to a muffin tin and bake for 5 minutes. After 5 minutes, lower the temperature to 350°F and bake an additional 10-12 minutes.
Let muffins cool in the tin about 5 minutes before transferring to a wire rack to cool completely.