In a large mortar, mash coriander seeds until they are broken down. Add chili flakes, garlic and onions, and mash until well-combined. Add thyme, zest and paprika. Add parsley until herbs release their aromas and essential oils. Stir in vinegar and oil. Keep at room temperature until ready to serve.
Leftover sauce should be refrigerated and lasts for a few weeks. Bring back to room temperature to serve.