Combine garlic, anchovy, capers, lemon zest, and red pepper flakes in a mortar and pestle or and grind into a rough paste.
Add lemon juice, parsley and basil and continue to grind, slowly adding olive oil until emulsified. Adjust seasoning to taste.
Serve this salsa verde at room temperature over freshly shucked or grilled oysters. Recipe can also be prepared using a small, bullet-style food processor for a smoother result.