Bring a large pot of lightly salted water to a boil. Cook spaghetti at a boil until cooked through but firm to the bite, about 12 minutes. Drain and transfer to a large bowl.

Put cubed Romano cheese in the bowl of a food processor; process until coarsely grated, about 30 seconds. Add garlic, and process until combined.

Add spinach, basil, walnuts, lemon juice, lemon zest, and salt to the processor. Process until the mixture forms a thick paste, scraping down sides as necessary.

With the food processor running, drizzle in olive oil and process until smoothly incorporated.