Preheat your oven to 350°F (175°C) and prepare a 9x13 inch baking pan by greasing and flouring it.

In a large mixing bowl, cream together softened butter and sugar until fluffy. Beat in the eggs one at a time and stir in the vanilla extract.

In a separate bowl, whisk together the flour, baking soda, salt, cinnamon, nutmeg, and cloves.

Gradually add the dry mixture to the wet mixture, mixing until just combined. Gently fold in the grated zucchini.

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

Bake for 25-30 minutes or until edges pull away from the pan and a toothpick comes out clean.

Allow the bars to cool in the pan on a wire rack completely before frosting.

In a bowl, whisk powdered sugar and milk until smooth. Adjust for thickness.

Spread frosting over cooled bars evenly and slice into squares for serving.