Add in additional milk as needed to get thick but pourable consistency.
Drizzle over the top of cooled bread, and grate a little more fresh lemon zest over the top of the glaze.
Let glaze set before slicing.
Notes
Zucchini: Use fresh, smaller zucchini for this bread. Large, overgrown zucchini can be dry and woody, which won't give you enough moisture for the bread. Also, there’s no need to peel the zucchini before use.
Flour: Be sure to properly measure the flour. I like to weigh the ingredients to ensure that the measurements are accurate (click "metric" immediately above the ingredients for the weights). If using measuring cups, sift or stir the flour. Then, lightly spoon into the measuring cup and level. This will help to avoid packing in the flour. Packing in the flour will give you a dry, heavy loaf of bread.
Butter: This recipe uses melted butter, so the batter can easily be mixed by hand. The butter should be just melted, not hot and bubbly or browned.
Vanilla extract: For more lemon flavor, use a combination of vanilla extract and lemon extract.
Milk: Using milk will give you a milder glaze. Using fresh lemon juice will give you tarter, more lemony glaze.