COOK spaghetti as directed on package, omitting salt.
MEANWHILE, gradually whisk dressing into peanut butter in small bowl. Stir in soy sauce; set aside. Stir-fry vegetables in medium nonstick skillet on medium-high heat 3 min. Add meat; stir-fry 3 to 4 min. or until done. Add dressing mixture; stir-fry 2 min. or until slightly thickened.
DRAIN spaghetti; place on platter. Top with meat mixture, cilantro and nuts.