Cook potatoes and cauliflower in boiling water in large saucepan 20 min. or until tender.
Meanwhile, cook chicken in large nonstick skillet sprayed with cooking spray on medium heat 3 to 4 min. on each side or until golden brown. Transfer to plate; cover to keep warm.
Add dressing, mushrooms and peppers to skillet; cook and stir 6 min. Add tomatoes; simmer 8 min. Return chicken to skillet; spoon sauce over chicken. Simmer 3 min. or until chicken is done (165 degrees F).
Drain potato mixture; return to pan. Add reduced-fat cream cheese; mash until potato mixture is fluffy. Serve topped with chicken, vegetables and basil.