In this hearty pasta dish, using spinach instead of basil makes for a more nutritious take on pesto.
Bring a large pot of salted water to boil. Prepare a large bowl of ice water; place a colander inside, resting in ice.
In batches, stir spinach into boilingwater. Cook until wilted and brightgreen, about 30 seconds. Transfer spinachto the colander (in the ice bath)to stop cooking. Reserve boiling water.Cool completely in ice bath, then liftcolander; squeeze spinach dry.
Cook pasta in reserved boiling water until al dente, according to package instructions. Save 1/2 cup pasta water; immediately drain pasta, and return to pot.
Meanwhile, place spinach, Parmesan, walnuts, garlic, and lemon zest and juice in a food processor. Process until a coarse paste forms. With motor running, add oil and 1/4 cup plain water; process until smooth and creamy, about 1 minute. Season with salt and pepper.
Add tomatoes and pesto to pasta; toss, adding reserved pasta water to coat pasta, if necessary. Taste and adjust salt and pepper, as needed. Serve with additional Parmesan, if desired.
Store in an airtight container in the fridge up to three days.