1. Heat a large skillet over medium heat. Add bacon; cook until crisp. Remove bacon from pan using a slotted spoon; crumble. Add chicken to drippings in pan; cook 2 minutes on each side or until done. Remove chicken from pan. Add baby spinach to pan; cook 30 seconds or until spinach begins to wilt, stirring constantly. Stir in balsamic vinegar.
2. Combine cheddar cheese and cream cheese in a small microwave-safe bowl. Microwave at HIGH 30 seconds or until melted; stir with a whisk until smooth. Stir in bacon. Spread cheese mixture evenly over cut sides of rolls. Divide tomatoes evenly over bottom halves of rolls; top with chicken and spinach mixture. Top sandwiches with top halves of rolls. Return pan to medium heat. Coat both sides of sandwiches with cooking spray. Add sandwiches to pan. Place a cast-iron skillet on top of sandwiches; press gently to flatten. Cook sandwiches 3 minutes on each side or until bread is toasted (leave skillet on sandwiches as they cook). Cut each sandwich in half diagonally.