A grilled chicken sandwich with a mustard ranch sauce.
In a small bowl combine ranch dressing, mustard, sugar, and vinegar. Mix well. Remove ½ cup of the dressing mixture and place it into a sealable ziplock bag with the chicken. Refrigerate and marinade for at least 30 minutes. Reserve the remaining dressing mixture for brushing the chicken.
Lightly grease the grates of an outdoor grill. Heat grill to medium heat. Remove chicken from the marinade and add to the grill. Grill for 6-7 minutes per side or until cooked through (the internal temperature has reached 165 degrees F.). While grilling brush with reserved marinade during the last few minutes of grilling. Top each chicken breast with a slice of mozzarella cheese. Grill until the cheese has melted. Remove from the grill.
Add the buns, cut-side down to the grill and cook until lightly toasted. Remove from the grill.
Top the rolls with grilled chicken, lettuce, and tomato.