In a food processor, combine Arugula, Parsley, Mint, and Marjoram. Pulse 2–3 times until coarsely chopped.
Add Fish Sauce and Red Wine Vinegar, then pulse again to incorporate.
With the machine running, slowly drizzle in Olive Oil until fully blended and slightly loose.
Taste and adjust with Lemon Juice, Kosher Salt, and Black Pepper as needed.
Notes
Storage: keep in an airtight jar in the fridge for up to 2 weeks, the vinegar and oil help it hold. Give it a stir before serving since it separates as it sits.