Cook chicken and onion in a skillet with a tight-fitting lid over mediumhigh heat for 8 minutes, stirring occasionally.
Add barbecue sauce, water and sugar; stir. Reduce heat to medium, cover and cook for 7 minutes or until chicken is cooked through.
Remove chicken from skillet; shred with forks or chop into small pieces; return to skillet and stir until evenly coated with sauce.
Cut baguette crosswise into 6 pieces, then cut each piece in half lengthwise. Fill each sandwich with chicken mixture and cheese slices.