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 mixing 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, grated zucchini, lemon juice, and lemon zest until combined.
Gradually add the dry ingredients to the wet mixture, stirring until just combined. Do not overmix.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.
While the cake is baking, prepare the glaze by whisking together the powdered sugar and lemon juice until smooth.
Once the cake is done, allow it to cool in the pan for about 10 minutes, then transfer it to a wire rack to cool completely.
Drizzle the lemon glaze over the cooled cake before serving.