Cook spaghetti according to package directions. , In a small bowl, whisk ricotta, Parmesan, oil, lemon zest, salt and pepper. Drain spaghetti, reserving 1/2 cup cooking liquid. Whisk the reserved 1/2 cup cooking liquid into ricotta mixture. , Return drained pasta to pan. Add ricotta mixture and toss to coat. Cook and stir over low heat or until heated through. Sprinkle with parsley and additional lemon zest.