Preheat the oven to 350°F (175°C) and prepare your baking pan.
In a large mixing bowl, whisk together the dry ingredients: flour, sugar, baking powder, baking soda, cinnamon, nutmeg, ginger, and salt.
In another bowl, combine the canned pumpkin, vegetable oil, eggs, and vanilla, mixing until smooth.
Gradually add the wet mixture to the dry ingredients, stirring gently until just combined.
In a separate bowl, blend the oats, brown sugar, cold butter, and cinnamon to create the crumble topping.
Pour the pumpkin batter into the prepared cake pan, spreading it evenly.
Sprinkle the crumble mixture generously over the pumpkin batter.
Bake for 45-50 minutes, or until a toothpick inserted in the center comes out clean.
Once baked, remove from the oven and let it cool in the pan for 10 minutes before transferring to a wire rack.
Serve warm or at room temperature, and enjoy the flavors of autumn.