Combine the dressing mix, oil and vinegar in a large, resealable plastic bag and mix together. Add chicken to bag, seal and shake to coat; work mixture into the meat.
Refrigerate to marinate for at least 1 hour, or overnight if possible.
Preheat oven to Broil/Grill.
Remove chicken from bag, discarding any remaining marinade, and broil for 10 to 15 minutes or until cooked through and no longer pink inside.
