The ridges in spiral-cut fusilli are ideal for catching this fresh green sauce, made from spinach and walnuts instead of basil and pine nuts.
Add spinach and 1 tablespoon water to a large skillet set over medium-high. Cook, stirring constantly, until spinach is wilted, about 3 minutes. In a food processor, combine spinach, walnuts, oil, and lemon zest. Process until mixture forms a smooth paste, scraping down bowl as needed. Season with salt and pepper.
In a large pot of boiling salted water, cook pasta until al dente. Reserve 2 cups pasta water; drain pasta. Return pasta to pot and add pesto, tossing to combine and adding enough pasta water to create a sauce that coats pasta. Transfer to a serving plate, top with pecorino, and serve immediately.