Preheat the oven to 350°F (180°C) and line a baking sheet with parchment paper.
In a large bowl, mix the pumpkin puree, sugar, vegetable oil, and egg until well combined.
Add the flour, baking powder, cinnamon, nutmeg, and salt to the wet ingredients. Mix until a soft dough forms.
In a separate bowl, combine the streusel topping ingredients - sugar, flour, butter, and cinnamon. Use a fork or pastry cutter to create a crumbly mixture.
Scoop tablespoon-sized dough balls onto the prepared baking sheet, spacing them apart.
Sprinkle the streusel topping over each cookie.
Bake for 12-15 minutes or until the edges are lightly golden.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring them to a wire rack to cool completely.
Notes
For an extra touch, drizzle a simple glaze made of powdered sugar and milk over the cooled cookies.