4 skinless boneless chicken breasts
1 tablespoon Dijon mustard
3 tablespoons vegetable or olive oil
1 tablespoon white or red wine vinegar
1/4 teaspoon dried thyme
4 large thin slices baked ham
4 thin slices Swiss cheese
Butterfly each chicken breast by halving it horizontally, but leaving one side attached, so that it opens into a large thin cutlet.
Whisk together the mustard, oil, lemon vinegar and thyme. On a plate coat the chicken with the marinade, stacking the breasts as they are coated. Cover the chicken and let it marinate in the refrigerator for 30 minutes to 3 hours.
Discard the marinade and grill the opened chicken breasts over hot coals for 5 minutes. Turn and top each with a slice of ham and Swiss. Cook another 5 minutes.