Make the gremolata. Place the parsley leaves, garlic, and lemon zest on a clean cutting board. Use a sharp chef’s knife or a mezzaluna to reduce the mixture to a fine mince. Keep chopping until all the ingredients are very finely chopped, fluffy, and uniform in size. Transfer the gremolata to a bowl.
Store leftovers. If you have any leftover gremolata, put it in a tightly lidded container and refrigerate it for up to a day. For longer keeping, stir in 1 to 2 tablespoons of extra-virgin olive oil, and store in the fridge in a lidded container for up to 4 days.