Preheat your oven to 350°F (175°C). Grease and flour a 9×9-inch baking pan.
In a large bowl, mix the cake mix, vegetable oil, milk, eggs, lemon juice, poppy seeds, and lemon zest. Beat on low speed for 30 seconds, then on medium speed for 2 minutes until well blended.
Pour the batter into the prepared pan and smooth the top.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cake to cool in the pan for 10 minutes before transferring to a wire rack to cool completely.
While the cake is cooling, prepare the lemon glaze. In a small bowl, whisk together the powdered sugar, lemon juice, and milk until smooth.
Drizzle the glaze over the cooled cake.