Preheat your oven to 350°F (175°C) and line a standard 12-cup muffin tin with paper liners or grease thoroughly.
Grate the zucchini using the medium holes of a box grater and place it in a clean kitchen towel. Squeeze firmly to remove excess moisture.
In a medium bowl, whisk together the flour, baking soda, baking powder, salt, cinnamon, nutmeg, cloves, and ginger until well combined.
In a large bowl, whisk together the sugar and oil until well combined. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract, then fold in the pumpkin puree until smooth.
Gradually add the dry ingredients to the wet ingredients, stirring just until combined. Do not overmix.
Gently fold in the drained zucchini and nuts (if using) with a rubber spatula.
Divide the batter evenly among the prepared muffin cups, filling each about ¾ full.
Bake for 20-22 minutes, or until a toothpick inserted into the center comes out clean with a few moist crumbs. The muffins should spring back when lightly touched on top.
Allow the muffins to cool in the pan for 5 minutes before transferring to a wire rack to cool completely.
For the optional glaze, whisk together powdered sugar, maple syrup, milk, and vanilla extract until smooth. Drizzle over cooled muffins.