Preheat your oven according to the instructions on the cake mix box. Prepare a 9×13-inch baking dish by greasing it lightly or lining it with parchment paper.

1. Prepare the cake batter according to the instructions on the box and bake in the preheated oven for the time specified.
2. While the cake is baking, prepare the lemon glaze. In a saucepan, combine the sugar, water, and lemon juice. Heat over medium heat, stirring occasionally, until the sugar is fully dissolved. Bring it to a boil and let it simmer for 2-3 minutes, then remove from heat.
3. Once the cake is finished baking, allow it to cool in the pan for about 10 minutes. Then, use a fork or a skewer to poke holes all over the top of the cake, ensuring you reach the bottom.
4. Pour the warm lemon glaze evenly over the cake, allowing it to soak into the holes. Let the cake cool completely at room temperature.
5. Once cooled, spread the whipped topping over the cake, covering it evenly.
6. Garnish with lemon zest or a few thin lemon slices if desired, then refrigerate for at least 2 hours (or overnight) to let the flavors fully meld.