1. Combine first 7 ingredients in a large zip-top plastic bag.
2. Add chicken; seal and marinate in refrigerator at least 30 minutes.
3. Remove chicken from bag; reserve marinade.
4. Place chicken on grill rack coated with cooking spray; cover and grill 10 minutes on each side or until chicken is done; baste occasionally with reserved marinade.
5. Combine orzo and next 4 ingredients in a bowl; toss gently to coat.
6. Serve chicken on top of orzo.
7. Garnish with fresh oregano sprigs, if desired.
8. Yield: 4 servings.