Prepare the Cake:

Preheat Oven:

Preheat your oven to 350°F (175°C). Grease and flour a 9x13-inch baking dish.

Make the Batter:

In a large mixing bowl, combine the lemon cake mix, instant lemon pudding mix, eggs, vegetable oil, water, lemon juice, and lemon zest. Beat with an electric mixer on medium speed until the batter is smooth and creamy.

Bake:

Pour the batter into the prepared baking dish and spread evenly. Bake for 35-40 minutes, or until a toothpick inserted into the center comes out clean. Allow the cake to cool completely.

Prepare the Lemon Filling:

Mix the Filling:

In a medium bowl, whisk together the sweetened condensed milk, fresh lemon juice, and lemon zest until thickened.

Assemble the Cake:

Poke the Cake:

Using the handle of a wooden spoon, poke holes all over the cooled cake. Pour the lemon filling over the cake, spreading it into the holes.

Add the Topping:

Spread the whipped topping evenly over the cake. Sprinkle with powdered sugar or lemon zest if desired.

Chill and Serve:

Chill:

Refrigerate the cake for at least 1 hour to allow the flavors to meld and the filling to set.

Serve:

Slice and serve cold, garnished with lemon slices or extra zest for a beautiful presentation.