Preheat the oven to 350°.
Line a 9 x 5 loaf pan with a strip of parchment paper and grease lightly with spray oil.
Using a stand mixer fitted with the paddle attachment (or a handheld mixer and a medium bowl), beat the mashed banana and oil on medium high until well combined.
Add the brown sugar. Continue beating on medium high until well combined.
In this order, add the flour and baking soda.
Use a fork and lighty mix the baking soda and flour together on top of the wet ingredients.
Use a spatula, fold the flour and baking soda into the wet ingredients until just combined. It is okay if there are a few pockets of flour.
Pour the batter into the loaf pan and spread into an even layer.
Sprinkle the remaining brown sugar on top of the batter. Using your hands, press the brown sugar into the batter slightly.
Bake for 50-55 minutes or until a toothpick comes out clean. Cool on a wire rack for 1-2 hours before slicing.
Use parchment paper to remove the loaf from the pan. Slice and enjoy!