Combine first 12 ingredients in a blender; process until well blended. Pour mixture into a large heavy-duty zip-top plastic bag; add onion and chicken. Seal bag; marinate in refrigerator 1 to 2 hours, turning bag occasionally.
Remove chicken from bag; discard marinade. Place chicken on grill rack coated with cooking spray. Grill chicken, covered, 5 minutes on each side or until done. Garnish with parsley and lime slices, if desired.