Mash the banana until only a few lumps remain and set aside.
Lower your oven rack to the third position up from the bottom. Preheat the oven to 375 degree F and line 4 center cups of a muffin pan with cupcake liners.
In a small bowl, add the flour, baking powder, baking soda, and salt and whisk to combine. Set aside.
In a medium sized bowl, whisk together the oil and sugar until blended.
Add the egg and vanilla to the sugar, and whisk until combined.
Pour the mashed banana into the egg and sugar mixture and whisk until fully incorporated.
Add the dry ingredients to the wet ingredients. Use a rubber spatula to fold the ingredients together until just mixed and no lumps or streaks of flour remain.
Divide the batter between the four prepped muffin cups. The cups will be very full.
Bake the muffins at 375 degrees F for 12-15 minutes until the tops are pointed and a toothpick inserted into the center comes out clean.