Preheat your oven to 350°F (175°C) and prepare a 9-inch round cake pan by greasing it lightly.

In a mixing bowl, whisk together the flour, baking powder, baking soda, pumpkin pie spice, and salt.

In another bowl, combine the granulated sugar, brown sugar, egg, pumpkin puree, vegetable oil, and vanilla extract until well mixed.

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

Pour the batter into the prepared cake pan and smooth the top.

In a separate bowl, combine the oats, chopped pecans, melted butter, and maple syrup to create the crumble topping.

Sprinkle the crumble topping over the cake batter evenly.

Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.

Remove from the oven and let cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Slice and serve the cake, optionally topped with whipped cream or vanilla ice cream.