Preheat oven to 350°F. Spray a bundt pan with cooking spray and set aside.
In a large bowl, beat together 1 cup orange juice, 1/3 cup vegetable oil, and 3 eggs until combined.
Add the 115.25 oz lemon cake mix to the wet ingredients. Mix until just moistened, then beat on medium speed for 2 minutes, scraping the bowl as needed.
Fold in 1 1/2 tablespoons poppy seeds and the zest from 1 orange and 1 lemon until evenly distributed.
Pour the batter into the prepared bundt pan and smooth the top. Bake for 30–35 minutes, or until a toothpick inserted into the center comes out clean.
Remove the cake from the oven and let it cool in the pan for 5 minutes. Then invert the cake onto a cooling rack and cool completely.
While the cake cools, whisk together 2 cups sifted powdered sugar and 2–3 tablespoons orange juice (start with 2 tablespoons and add up to 3 tablespoons to reach a pourable icing consistency).
Spoon or pour the icing over the completely cooled cake. Top with the additional orange and lemon zest.