Preheat your oven to 350°F (175°C). Grease a 9x13 baking dish.
In a large mixing bowl, combine the pumpkin puree, vegetable oil, sugar, eggs, and vanilla extract. Mix until well combined.
In another bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, and nutmeg. Gradually add the dry ingredients to the wet ingredients, mixing just until combined.
Pour the batter into the prepared baking dish and spread it out evenly.
For the crumb topping, combine the brown sugar, flour, and cinnamon in a small bowl. Add the melted butter and mix until the mixture is crumbly. Sprinkle the crumb topping evenly over the batter.
Bake in the preheated oven for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool before serving.