In a medium bowl, mix chopped parsley, chopped toasted walnuts, chopped rosemary, chopped garlic cloves, the zest of 1 lemon, Kosher salt.
Stir in extra virgin olive oil, depending on how thick or thin you want the gremolata to be. Taste and adjust seasoning. Serve on top of pastas, meats, or vegetables.
– To make-ahead: Gremolata can be made up to 3 days in advance. You can also freeze it for up to 2 months.