Prep the herbs. Rinse the cilantro and parsley well, then pat thoroughly dry.
Remove any thick, woody stems, but keep tender stems for extra flavor and body.
Pulse the base ingredients. In a food processor, add the nuts, garlic, lemon zest, and red pepper flakes. Pulse a few times until the nuts are finely chopped, not paste-like.
Add herbs and cheese. Add the cilantro, parsley (if using), Parmesan, and salt. Pulse in quick bursts to start breaking everything down.
Stream in the oil. With the machine running, slowly drizzle in 1/3 cup olive oil.
Stop and scrape down the sides. If the pesto looks dry or too thick, add more oil a tablespoon at a time until spreadable and glossy.
Adjust the acidity. Add the lemon juice and pulse again. Taste and adjust with more salt, pepper, and lemon if needed.
It should be bright, savory, and balanced.
Serve. Spread on warm, crusty baguette slices. Finish with a sprinkle of flaky salt, extra Parmesan, or a drizzle of olive oil if you like.