Preheat the oven to 350°F (175°C). Grease a cake pan.
In a bowl, whisk together gluten-free flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
In another bowl, beat sugar and butter until creamy. Add eggs, pumpkin, and vanilla. Mix until combined.
Gradually add the dry ingredients to the wet mixture, stirring until smooth.
In a separate bowl, combine sugar, gluten-free flour, cinnamon, and butter for the streusel. Mix until crumbly.
Pour the cake batter into the prepared pan. Sprinkle the streusel topping evenly over the top.
Bake for 35-40 minutes or until a toothpick comes out clean.
Cool for 10 minutes, then transfer to a cooling rack.