While a cheese grater might seem like a good option, often the grates are too deep or too shallow to get the best bit of the citrus, unless you have a grater with a built-in zester, which many multi-sided graters feature. If you don’t have a zester, it’s best to use a vegetable peeler or paring knife and cut a strip of yellow skin off of the lemon and dice it into very small pieces, though this won’t be as effective as using a zester.