Preheat oven to 350 F. Line or grease 24 mini muffin pan, or 12 regular muffin pan wells and set aside. In a mixing bowl, whisk together the flour, baking powder, salt, and pumpkin pie spice.
In another mixing bowl, whisk together the pumpkin, eggs, oil, brown sugar, and vanilla until smooth. Sprinkle the flour mixture over the wet mixture and fold until just combined.
Spoon the batter into the muffin liners, about 3/4 full. Make the streusel topping: combine the flour, sugar, and cinnamon in a bowl. Cut in the butter and use a fork or pastry fork to mix until crumbly.
Spoon the streusel evenly over each portion of the muffin batter. Bake for 11 minutes for mini muffins or 18-20 minutes for regular sizes. Remove as soon as middle springs back when gently touched in the middle as to not over-bake them.
Allow to sit in the pan no longer than 5 minutes. Use a spoon to remove each one and set on a cooling rack so they don't continue baking in the hot pan.