1Put oven rack in middle position and preheat oven to 350 degrees. Put liners in muffin cups.
2Whisk together flour and baking powder in a small bowl. Whisk together pumpkin, oil, eggs, pumpkin pie spice, 1 1/4 cups sugar, baking soda, and salt in a large bowl until smooth, then whisk in flour mixture until just combined. Stir together cinnamon and remaining 1 tablespoon sugar in another bowl.
3Fill each muffin cup about three-quarters full, and then sprinkle tops with cinnamon-sugar mixture. Bake until puffed and golden brown and a toothpick inserted into center of a muffin comes out clean, 25 to 30 minutes.
4Cool in a pan on a rack 5 minutes, and then transfer muffins from pan to a rack to cool to warm or room temperature. Garnish with powdered sugar if desired.