Heat oven to 350°F (325°F for dark or nonstick pan). Grease and lightly flour 12-cup fluted tube cake pan, or spray with baking spray with flour.
In large bowl, beat cake mix, 1 tablespoon orange peel, water, 1/2 cup orange juice, oil and eggs with electric mixer on low speed 30 seconds, then on medium speed 2 minutes, scraping bowl occasionally. Stir in poppy seed. Pour into pan.
Bake as directed on box for 12-cup fluted tube pan. Cool 15 minutes; remove from pan to cooling rack or heatproof serving plate. Cool completely, about 2 hours.
In small bowl, mix powdered sugar, 1/4 teaspoon orange peel and 1 tablespoon orange juice. Stir in additional orange juice, 1 teaspoon at a time, until glaze is smooth and consistency of thick syrup. Spread glaze over top of cake, allowing some to drizzle down sides. Garnish with additional orange peel. Store loosely covered.