Preheat the oven to 350 degrees F. Prepare the cake mix according to package instructions except use 2 tablespoons fewer of water and add the lemon juice instead. Stir the grated lemon rind into the batter, mixing in well. Bake in a sprayed or greased 9×13-inch pan. Baking time will be 35-40 minutes or until a toothpick comes out clean.
Meanwhile, in a medium bowl, beat the egg whites and cream of tartar until soft peaks form. Gradually beat in the sugar until stiff peaks form. Let the cake cool for 5 minutes. Then spread the meringue over the top. Make sure it completely covers the top of the cake, and make a lot of peaks and valleys to form an attractive topping. Return the cake to the oven for 12-15 minutes or until meringue is golden. Let cool completely before serving.