Toast the walnuts. Warm a dry skillet over medium heat. Add the walnuts and toast, shaking the pan, until fragrant and slightly darker, about 3–4 minutes. Let them cool to avoid melting the spinach in the blender.

Boil the pasta. Bring a large pot of generously salted water to a boil. Cook the pasta until just shy of al dente. Reserve 1 cup of pasta water, then drain.

Build the pesto base. In a food processor, add the cooled walnuts, garlic, lemon zest, and a pinch of salt. Pulse until finely chopped. This releases flavor and keeps the final sauce smooth.

Add greens and cheese. Add spinach, basil, and grated Parmesan. Pulse to combine, scraping down the sides as needed. You want a rough, even mixture before adding oil.

Stream in olive oil. With the machine running, slowly pour in 1/3 cup olive oil. If it looks thick or dry, add more oil or a splash of reserved pasta water until it becomes creamy and scoopable.

Season and brighten. Add 1 tablespoon lemon juice and a few grinds of black pepper. Taste and adjust with more lemon, salt, or a pinch of red pepper flakes for heat.

Toss with pasta. Return the hot pasta to the pot. Add the pesto and 1/4 cup of reserved pasta water. Toss over low heat for 30–60 seconds until the sauce glossy-coats the noodles. Add more water if needed to loosen.

Finish and serve. Top with extra Parmesan, a drizzle of olive oil, and a crack of pepper. Serve immediately while it’s bright and aromatic.