COOK spaghetti as directed on package, omitting salt.
MEANWHILE, blend 1 can tomatoes, peppers and cream cheese in blender until smooth. Heat large nonstick skillet on medium-high heat. Add chicken and onions; cook 8 min. or until chicken is evenly browned, stirring occasionally. Stir in cream cheese sauce and remaining tomatoes. Simmer on medium heat 5 min. or until chicken is done, stirring occasionally.
DRAIN spaghetti; toss with sauce.