COOK chicken, onions and mushrooms in large nonstick skillet on medium-high heat 10 min. or until chicken is done (165°F), stirring onion mixture occasionally and turning chicken after 5 min. Transfer chicken to plate; cover to keep warm. Continue cooking onion mixture 3 to 5 min. or until golden brown, stirring occasionally.
ADD Worcestershire sauce to onion mixture in skillet; mix well. Reduce heat to low. Return chicken to skillet; spoon onion mixture over chicken.
MIX stuffing mix and hot water; spoon around edge of skillet. Sprinkle with cheese; cover. Cook 5 min. or until cheese is melted.