The easiest way to clean a zester is to immediately wipe off the excess zest with your finger tips from the handle side out towards the zesting edge on both sides (so you won't cut your fingers on the blades). Rinse right away with water. Then you'll easily be able to wash with soap and water when ready to. By doing this, it will keep any of the remaining zest from drying in the holes which will save a lot of scrubbing time.
This is what I've done for as long as I can remember. It works great for easy cleanup on graters and microplane zesters, whether using for citrus, garlic, cheese, or any other foods too :-)
By Deeli from Richland, WA
A good tip for us zester challenged folk.