COOK pasta as directed on package, omitting salt.
MEANWHILE, cook chicken in dressing in large nonstick skillet on medium-high heat 5 to 7 min. or until chicken is done, stirring occasionally. Stir in vegetables; cover. Simmer on medium heat 5 min. or until vegetables are crisp-tender.
MICROWAVE VELVEETA and milk in small microwaveable bowl on HIGH 2 to 3 min. or until VELVEETA is melted and mixture is well blended, stirring after 1-1/2 min. Add to chicken mixture; mix lightly. Serve over pasta.