COOK chicken and onions in large nonstick skillet on medium-high heat 8 min., stirring occasionally.
ADD barbecue sauce, water and sugar; stir. Cover; cook on medium heat 7 min. or until chicken is done (165ºF).
REMOVE chicken from skillet. Shred with fork or chop into small pieces. Return to skillet; stir to coat with sauce. Cut baguette into 4 pieces; cut each piece lengthwise in half. Fill with chicken mixture and Singles.