Put oven in middle position and preheat oven to 350°F. Put liners in muffin cups and spray with non-stick spray. Whisk together flour, baking powder, salt, and spices. Set aside. Whisk together pumpkin, oil, eggs, pumpkin, brown sugar, vanilla extract and baking soda in a large bowl until smooth, then whisk in flour mixture until just combined. Fold in any additions, such as chips, nuts, or raisins. In a small bowl squish the butter, sugar, flour and cinnamon together with a fork until it resembles a course meal. Sprinkle on top of each muffin. Bake for 20-25 minutes until an inserted toothpick comes out clean.