Preheat your oven to 350°F. Line a 12 count muffin tin with paper liners, and set aside. In a medium bowl, combine your flour, baking powder, baking soda, and salt. Whisk to combine. Set aside to work on the wet ingredients.
In a large bowl, add in your peeled bananas. Mash the bananas until they're completely broken up into a puree consistency (a few clumps here and there are fine). Add in your sugar, egg, and vegetable oil. Whisk well to combine.
Combine the wet and dry ingredients. Mix together until just combined. Take care not to over mix or the muffins will end up dense!
Portion out the banana muffin batter into your prepared muffin tin. Bake in the center of your preheated 350°F oven for 20 to 25 minutes, or until the muffins turn a deep golden brown color and a skewer inserted into the center of one muffin comes out clean. Cool for 5 to 10 minutes in your muffin tin, then transfer to a wire rack to cool completely. Serve warm or at room temperature.