Preheat your oven to 350°F (175°C). Grease your 9x13 inch baking pan with oil or non-stick spray, and lightly flour it to prevent sticking. Alternatively, line the pan with parchment paper for easy removal.
In a large bowl, whisk together 2 cups of all-purpose flour, 1 teaspoon baking powder, 1 teaspoon baking soda, 1 teaspoon ground cinnamon, 1/2 teaspoon ground nutmeg, and 1/2 teaspoon salt. Set aside.
In another large bowl, beat 1 cup granulated sugar, 1 cup packed brown sugar, and 1 cup vegetable oil until combined. Add 4 large eggs, one at a time, beating well after each addition. Stir in 1 can (15 oz) pumpkin puree and 1 teaspoon vanilla extract until smooth.
Gradually add the dry ingredients to the wet mixture, stirring just until combined. Avoid overmixing to keep the cake tender. Fold in 1 cup chopped pecans gently.
Pour the batter into the prepared pan and smooth the top with a spatula. Bake for 35 to 40 minutes, or until a toothpick inserted into the center comes out clean or with just a few moist crumbs attached.
Allow the cake to cool completely in the pan on a wire rack before slicing. This ensures it sets properly and slices cleanly. Serve plain, dusted with powdered sugar, or alongside a dollop of whipped cream or cream cheese frosting for extra indulgence.