Preheat the oven to 350°F (175°C). Grease and flour a 9x13 inch baking dish.

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

In another bowl, mix the granulated sugar, brown sugar, pumpkin puree, vegetable oil, and eggs until well combined.

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

Pour the batter into the prepared baking dish and smooth the top.

Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.

In a separate bowl, combine the sliced apples with cinnamon and set aside.

In another bowl, mix the oats, brown sugar, flour, and melted butter until crumbly.

Spread the apple mixture evenly over the baked pumpkin spice cake.

Top with the oat mixture and bake for an additional 15-20 minutes until the apples are tender and the topping is golden brown.

Let cool slightly before serving.