Preheat your oven to 350°F (175°C) and grease your 9x13 inch baking dish.
In a mixing bowl, whisk together the all-purpose flour, baking powder, baking soda, ground cinnamon, and salt.
In another bowl, combine the granulated sugar, brown sugar, and vegetable oil. Mix until combined.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.
Gradually add the dry ingredients into the wet mixture until just combined. Be careful not to overmix.
Fold in the grated zucchini and nuts (if using) with a rubber spatula until evenly distributed.
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. Allow the cake to cool in the pan for about 10 minutes, then transfer to a cooling rack to cool completely.
To make the cream cheese frosting, beat the softened cream cheese and butter together until creamy and well blended.
Gradually add the powdered sugar, incorporating fully, then mix in the vanilla extract. If the frosting is too thick, add milk one tablespoon at a time until the desired consistency is reached.
Once the cake is completely cool, spread the cream cheese frosting evenly over the top of the cake.
Cut into 12 pieces and enjoy!