Place 8 cookies, flat-sides up, on microwaveable plate; top with next 3 ingredients.
Microwave on HIGH 30 sec. or until chocolate is almost melted. Cover with remaining cookies; press down lightly to secure. Microwave 30 sec. or until cookies are warmed and chocolate and marshmallows are melted.
Serve warm. Or, cover and refrigerate 5 to 10 min. or until filling is set.