Preheat the oven to 350°F. Spray a 5x3-inch mini loaf pan with nonstick spray.
In a medium bowl, add the flour, brown sugar, baking powder, pumpkin pie spice, baking soda and salt. Whisk to combine. Set aside.
In a small bowl, combine the banana, buttermilk, egg, butter and vanilla. Whisk to combine. Pour the wet ingredients into the dry ingredients and use a spatula to mix until just combined, about ten strokes. Do not overmix.
Transfer the batter to the prepared pan. Bake 30 to 35 minutes or until the bread springs back when gently pressed in the center and the top is golden brown. Cool in the pan for 3 minutes, then transfer to a wire rack to cool to room temperature.