In a high-speed blender or food processor, add the garlic, pine nuts, basil, and lemon zest. Pulse until the mixture becomes sandy.
Season with salt and red pepper flakes and add the lemon juice. With the blender running on low, begin to stream in the olive oil. Continue to blend, scraping down the sides intermittently, until well combined. You still want a little texture!
Note: If the mixture is too thick, stream in additional olive oil, 1 tablespoon at a time.
Transfer to a bowl, then stir in the grated Parmesan (if using). Serve & enjoy however you prefer!