How to Make It
Heat a grill pan over medium-high heat.
Combine first 6 ingredients; spread evenly over 4 bread slices. Top evenly with turkey, watercress, cheese, and remaining 4 bread slices.
Coat grill pan with cooking spray. Arrange 2 sandwiches in pan. Place a cast-iron or heavy skillet on top of sandwiches; press gently to flatten. Cook 2 minutes on each side (leave cast-iron skillet on sandwiches while they cook). Repeat procedure with remaining 2 sandwiches.