1. Bring large pot of heavily salted water to boil over high heat. Add pasta and cook according to package directions or until al dente.
2. Meanwhile, make pesto. Place half of spinach and all of pine nuts and garlic in a food processor fitted with blade attachment. Pulse, scraping down sides of bowl with rubber spatula as needed, until coarsely chopped, about 10 (1-second) pulses. Scrape down sides of bowl. Add remaining spinach and pulse until coarsely chopped, about 20 (1-second) pulses, scraping down sides of bowl as needed.
Add measured Parmesan, lemon zest and juice, measured salt, and measured pepper and process until combined, about 30 seconds. Scrape down the sides of bowl.
With motor running, slowly pour in oil and process until a smooth paste forms, about 30 seconds; set pesto aside in the food processor.
3. When pasta is ready, reserve 1/2 cup of cooking water, then drain pasta and return it to pot. Place pot over low heat, add pesto and 1/4 cup of reserved cooking water, and stir to combine. Cook, stirring occasionally, until pasta is well coated, adding more pasta water as needed to reach desired consistency. Taste, season with additional salt and pepper as needed, and serve with Parmesan on the side.