Preheat oven to 350 degrees F. Spray muffin pan cups with non-stick cooking spray or line with liner cups. Set aside.
To a large mixing bowl, add melted butter, sugar, eggs and vanilla and stir to combine thoroughly. Stir in grated zucchini.
Add flour, baking soda, cinnamon, nutmeg, salt and cloves (if using). Stir until JUST combined, being careful not to over mix. Just stir until there are no streaks of flour remaining.
Scoop batter into prepared muffin pan, filling the cups almost to the top. Bake about 20-23 minutes, until golden brown and a toothpick inserted in the center comes out with only a few moist crumbs on it.
Let muffins cool in the pan a few minutes, then remove them to a wire rack to continue cooling.