Preheat the oven to 350°F (175°C). Grease and flour a 9-inch round or square baking pan.
In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, salt, and ground cinnamon. Set aside.
In a large bowl, beat the softened butter and granulated sugar together with an electric mixer on medium speed until light and fluffy, about 3 minutes.
Add the eggs one at a time, beating well after each addition. Mix in the vanilla extract.
Reduce the mixer speed to low and add the dry ingredients in three additions, alternating with the sour cream, beginning and ending with the dry ingredients. Mix just until combined.
Fold in the grated zucchini, lemon zest, and fresh lemon juice gently with a spatula until evenly distributed.
Pour the batter into the prepared baking pan and spread it evenly.
Bake for 40 to 45 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 15 minutes, then transfer it to a wire rack to cool completely.
In a small bowl, whisk together the powdered sugar and 1 tablespoon fresh lemon juice until smooth to make the lemon glaze.
Drizzle the lemon glaze over the cooled cake before serving.