Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or grease the muffin cups with non-stick spray.
In a small bowl, combine the flour, brown sugar, and pumpkin pie spice for the streusel. Add the cold, cubed butter and use a pastry cutter or your fingers to work the butter into the dry ingredients until the mixture resembles coarse crumbs. Set aside.
In a large mixing bowl, whisk together the mashed bananas, pumpkin puree (squeeze the excess moisture out of it) , granulated sugar, brown sugar, oil, eggs, and vanilla extract until smooth and well combined.
Gradually add the dry ingredients to the wet ingredients, mixing just until combined. Be careful not to overmix; the batter should be slightly lumpy.
Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
Generously sprinkle the streusel topping over each muffin, pressing it down lightly so it sticks to the batter.
Bake in the preheated oven for 18-22 minutes, or until a toothpick inserted into the center of a muffin comes out clean or with a few moist crumbs.
Allow the muffins to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely.
