Pierce potatoes in several place with fork. Microwave on HIGH 12 to 14 min. or until tender, turning after 7 min. Cool 5 min.
Cut potatoes lengthwise in half; scoop out centers into bowl, leaving 1/4-inch-thick shells. Mash potato centers lightly. Add sour cream, broccoli, chicken and 1/2 cup cheese; mix well.
Spoon mashed potato mixture into potato shells; sprinkle with remaining cheese. Place on microwaveable plate. Microwave 2 min. or until heated through.
Meanwhile, cook gravy in saucepan on medium heat until heated through, stirring occasionally.
Drizzle gravy over potatoes before serving.