Preheat your oven to 350°F (175°C). Grease and flour a 9-inch round cake pan.

In a bowl, whisk together the flour, baking powder, baking soda, salt, cinnamon, nutmeg, and ginger. Set aside.

In another bowl, mix together the pumpkin puree, sugar, vegetable oil, eggs, and vanilla extract until smooth.

Gradually add the dry mixture to the wet mixture, stirring until just combined.

Transfer the batter into your prepared cake pan, spreading it evenly.

In a small bowl, mix together the brown sugar, flour, and cinnamon. Cut in the cold butter until it resembles coarse crumbs.

Stir in the chopped nuts if you’re using them.

Sprinkle the crumble topping generously over the batter in the pan.

Place the cake in the preheated oven and bake for 30-35 minutes, or until a toothpick inserted in the center comes out clean.

Once baked, let it cool slightly in the pan before transferring to a wire rack to cool completely.