With a sharp knife, make several incisions in chicken. Insert pieces of garlic and rosemary. Place chicken in a flameproof dish.
In a bowl, mix together 2 tablespoons olive oil with lemon peel and juice, wine, salt and pepper. Pour over chicken breast halves and marinate 45 minutes. Preheat broiler.
Place chicken breast halves, skin-sides down in a dish. Broil 5 minutes. Turn chicken over and spoon marinade over chicken; broil 10 minutes longer or until skin is crisp and brown. Beat together mustard, vinegar, sugar, salt and pepper and remaining oil. Add any cooking juices from pan and spoon over chicken to serve.