Preheat your oven to 350°F (175°C) and grease the 9x13-inch baking dish.
In a mixing bowl, combine the flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Whisk until well mixed.
In another mixing bowl, blend the granulated sugar, brown sugar, and vegetable oil until creamy. Add the eggs one at a time, beating well after each addition.
Stir in the pumpkin puree and vanilla extract until everything is combined.
Gradually add the dry ingredient mixture to the wet ingredients, mixing until just combined. If desired, fold in the chopped pecans for added texture.
Pour the batter into the prepared baking dish and spread evenly.
Bake in the preheated oven for approximately 50 minutes or until a toothpick inserted in the center comes out clean.
Once baked, remove the cake from the oven and let it cool in the pan for about 15 minutes before transferring it to a cooling rack.
Serve the cake warm or at room temperature with whipped cream on top, if desired.