Cook first 5 ingredients in saucepan on low heat 3 min. or until heated through, stirring frequently. Remove from heat.
Cook chicken in large skillet sprayed with cooking spray on medium-high heat 5 min. or until lightly browned, stirring frequently. Add 1/4 cup peanut sauce; stir to evenly coat chicken with sauce. Cook 2 min. or until chicken is done, stirring constantly. Remove from heat.
Toss lettuce with carrots and tomatoes in large bowl; top with chicken. Drizzle with remaining peanut sauce just before serving.