HEAT dressing in large saucepan on medium-high heat. Add chicken and onions; cook 5 min., stirring occasionally.
ADD tomatoes, broth, water, peas and carrots and chili powder; stir. Bring to boil. Reduce heat to medium; simmer 8 min. or until chicken is cooked through and onions are tender. Meanwhile, preheat broiler.
LADLE soup into four ovenproof serving bowls; top with cheese. Broil, 6 inches from heat source, 2 to 3 min. or until cheese is melted.