Preheat the oven to 350°F (175°C) and grease and flour a 9x13 inch baking pan.
In a medium bowl, combine the flour, baking powder, baking soda, salt, and cinnamon. Whisk the dry ingredients together until well mixed.
In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3-5 minutes.
Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract, lemon zest, and lemon juice.
Gradually add the dry ingredients to the wet mixture, stirring just until combined.
Fold in the grated zucchini and nuts (if using) until evenly distributed throughout the batter.
Pour the batter into the prepared baking pan, spreading it evenly.
Bake in the preheated oven for 40-45 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack to cool completely.
Dust the top with powdered sugar if desired, slice, and serve.