Preheat the oven to 350°F (175°C). Grease a 9×5-inch loaf pan or line it with parchment paper.
In a large mixing bowl, mash the ripe bananas with a fork until smooth.
Add the melted butter to the mashed bananas and mix well.
Stir in the granulated sugar and brown sugar until combined.
Beat in the eggs one at a time, then add the vanilla extract and mix thoroughly.
In a separate bowl, whisk together the oat flour, baking soda, salt, and ground cinnamon.
Gradually add the dry ingredients to the wet ingredients, stirring gently until just combined. Do not overmix.
Pour the batter into the prepared loaf pan and smooth the top with a spatula.
Bake for 50 to 60 minutes, or until a toothpick inserted into the center comes out clean.
Remove the banana bread from the oven and let it cool in the pan for 10 minutes.
Transfer the bread to a wire rack to cool completely before slicing.