HEAT dressing in large saucepan on medium-high heat. Add chicken and onions; cook 5 min., stirring occasionally.
ADD all remaining ingredients except cheese; stir. Bring to boil; simmer on medium heat 8 min. or until chicken is done and onions are tender. Meanwhile, heat broiler.
LADLE soup into 6 ovenproof bowls; top with cheese. Broil, 6 inches from heat, 2 to 3 min. or until cheese is melted.