Beat together the balsamic vinegar, chicken stock, sugar, garlic, seasoning, put the chicken breasts in the marinade and marinate for 10 minutes on each side. You can immediately cut into slices.
Heat the olive oil in a large skillet over medium heat. Remove the chicken from the marinade. Place the chicken in a preheated pan and cook for about 7 minutes on each side.
Pour marinade in a pan and cook until it thickens slightly.