Follow package directions carefully for baking turkey (while still frozen), allowing last 30 minutes of baking for adding glaze. (A 12-lb. frozen turkey should take 3 1/2 to 4 hours to reach 170° in the breast.)
Combine jelly and mustard in a small saucepan, stirring well. Bring glaze mixture to a boil; boil 1 minute or until jelly is melted. Remove from heat. Set aside 1 cup glaze for serving.
When ready to apply glaze to turkey, carefully cut open top of oven bag, watching out for hot steam and juices. Pull bag away from top of turkey. Brush remaining 2/3 cup glaze over turkey in 2 additions during last 30 minutes of baking. Serve turkey with reserved 1 cup glaze.