HEAT oven to 375ºF.
HEAT vinaigrette in large skillet on medium heat. Add vegetables and garlic; cook 3 to 5 min. or until crisp-tender, stirring occasionally. Reserve 1 cup vegetable mixture. Stir 1/2 cup cheese into remaining vegetable mixture.
PLACE chicken thighs between 2 sheets of plastic wrap; pound to 1/2-inch thickness. Top each thigh with 2 Tbsp. vegetable mixture; roll up. Secure with wooden toothpicks or tie with string. Place on wire rack placed in 17x11-1/2-3/4-inch pan. Mix Miracle Whip and mustard; brush onto chicken.
BAKE 40 to 50 min. or until done (170ºF). Meanwhile, bring chicken broth to boil in medium saucepan. Stir in couscous and reserved vegetables. Remove from heat. Let stand 5 min.
SERVE couscous with chicken. Sprinkle with remaining cheese.