The orange part of the peel packs the most flavor. So grate only the bright orange skin and avoid the bitter-tasting white layer.
In a rush? In small microwavable bowl, microwave 1/2 container Betty Crocker® Rich & Creamy vanilla frosting with 1/4 teaspoon grated orange peel uncovered on High 15 to 25 seconds. Stir, then pour over cake.