POUR 1-1/2 qt. dressing (or 1-1/2 Tbsp. dressing for trial recipe) over chicken in non-reactive pan; turn chicken over to coat both sides of each breast. Refrigerate 2 hours to marinate. Remove chicken from marinade; discard marinade.
GRILL chicken on medium heat 3 to 4 min. on each side or until chicken is done (165°F). Keep warm.
FOR each serving: Fill 2 bread slices with 3 spinach leaves, 1 cheese slice, 1 chicken breast and 1 roasted pepper half. Brush outside of sandwich with 1-1/2 Tbsp. of the remaining dressing.
HEAT flat-top grill to 350°F. Add sandwich; cook 1 min. on each side or until sandwich is golden brown on both sides and cheese is melted.