In a pot cook pasta according to package directions. Drain, reserving 1 cup pasta water. Return pasta to pot.
Meanwhile, in a large skillet heat oil 2 minutes over medium-high heat. Add pistachios and garlic; cook 2 minutes or until lightly toasted. Stir ricotta, salt, and 1/2 cup pasta water into skillet until smooth and heated through. Transfer sauce to pot; stir in Parmesan. Add remaining pasta water; toss pasta until sauce is creamy. Gently toss in arugula. Top with black pepper and additional pistachios.