Preheat your oven to 350°F (180°C), or 160°C if using a fan oven, and line a muffin tin with paper liners or grease the wells well.
In a large bowl, combine the flour, pumpkin spice, baking powder, and salt. Stir to mix the dry ingredients thoroughly.
In a separate bowl, mash the banana with a fork (or mash on a cutting board then add), then add the pumpkin puree, granulated sugar, brown sugar, egg, vegetable oil, milk, and vanilla extract.
Add the dry ingredients into the wet ingredient mixture, stirring just until everything is combined and there are no streaks of flour.
Use a cookie scoop or a spoon to divide the batter into muffin cups.
Bake the muffins in the preheated oven for 20 minutes or until a toothpick inserted into the center of a muffin comes out clean or with just a few moist crumbs.
Allow the muffins to cool in the tin for 5 minutes, then transfer them to a wire rack to cool completely.