While rice is cooking, heat large nonstick skillet sprayed with cooking spray on medium heat. Add chicken and onions; sprinkle with oregano. Cook chicken 3 minute on each side or until chicken is lightly browned on both sides and onions are crisp-tender.
Add tomatoes, dressing and garlic; stir gently. Continue to cook 4 to 6 minute or until chicken is cooked through (165ºF), turning chicken after 3 minute Stir in olives.