Preheat the oven to 375°F. Line a muffin pan with liners or spray with nonstick spray.
Whisk the flour, sugar, pumpkin spice, cinnamon, baking soda, baking powder and salt in a large bowl.
Stir in the pumpkin, oil, eggs and vanilla and mix just until combined. Do not overmix. Add in mix-in's if desired.
Add the batter to the prepared muffin pan using a large cookie or ice cream scoop. Fill the liners 2/3 the way full.
For the streusel topping, combine the flour, brown sugar, pumpkin spice and butter in a bowl. Use a pastry cutter or forks to cut the butter. Mix until it has formed crumbs. Then evenly spread across the muffins.
Bake for 20 minutes, or until a toothpick comes clean. Remove from oven and allow to cool on a cooling rack.
Store the muffins in an airtight container for up to 3 days for freeze for up to 3 months.