Preheat oven to 350, line a mini muffin pan with parchment paper liners (or use a silicone muffin pan).
Mix wet ingredients (pumpkin puree, Greek yogurt, egg, maple syrup) in a large bowl until smooth.
Add dry ingredients (flour, baking powder, baking soda, pumpkin pie spice, salt) and stir to combine. Do not over mix.
Fill mini muffin pan equally, this recipe makes 24 mini muffins.
Optional: if making crumble topping, mix all ingredients together in a small bowl. IT should come together but still be a little crumbly. Add a 1 tsp of crumble to top of each muffin, press in a little (to avoid it falling off).
Bake at 350 for 12-15 minutes.
Allow to cool, store in airtight container or freeze (see storage instructions above).