HEAT large nonstick skillet sprayed with cooking spray on medium heat. Add chicken and onions; sprinkle with oregano.
COOK chicken 3 min. on each side or until chicken is lightly browned on both sides and onions are crisp-tender. Add tomatoes, dressing and garlic; stir gently. Cook 4 to 6 min. or until chicken is done (170ºF), turning chicken after 3 min. Stir in olives.
SPOON rice onto platter; top with chicken and sauce.