Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking pan.

In a medium bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon. Set aside.

In a large bowl, cream the softened butter and granulated sugar together until light and fluffy, about 3-4 minutes.

Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract.

Gradually add the dry ingredients to the wet mixture, mixing until just combined.

Fold in the grated zucchini, grated carrots, and walnuts (if using) until evenly distributed.

Pour the batter into the prepared baking pan and spread it evenly.

Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean. Let it cool in the pan for 10 minutes before transferring to a wire rack to cool completely.

Once cooled, dust the top with powdered sugar before serving.