PLACE pistachios in food processor; process until chopped. Add spinach, lemon and garlic; pulse a few times until combined. With processor running, gradually pour in oil until a smooth sauce forms. Add cheese; pulse a few times. Season with salt, if desired. Season with pepper.
PREPARE pasta according to package directions, reserving ½ cup cooking water. Combine pasta, ¼ cup cooking water and pesto in large bowl; toss gently to coat. Thin with additional cooking water if desired. Add tomatoes, tossing gently to incorporate. Serve topped with additional pistachios.
