ADD water to drink mix in large bowl; stir until mix is dissolved. Add yogurt; beat with mixer until blended. Whisk in COOL WHIP until blended. Freeze, if necessary, until mixture is thick enough to mound.
SPOON into crust.
FREEZE 4 hours or until firm. About 15 min. before serving, remove pie from freezer; let stand at room temperature until pie can easily be cut.