Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.
In a large bowl, combine the cake mix, water, vegetable oil, and eggs. Beat on low speed for 30 seconds, then on medium speed for 2 minutes, until well combined.
Stir in the lemon zest and lemon juice.
Pour the batter into the prepared pan and smooth the top with a spatula.
Bake for 30-35 minutes, or until a toothpick inserted into the center comes out clean.
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 and allow it to set before serving.