Heat oven to 350 F Grease 13x9 inch pan. In large bowl, combine cake mix, 1/2 cup margarine, and egg; mix at low speed until crumbly. Press mixture in bottom of greased pan.
In medium saucepan combine 1 1/3 Cups sugar, cornstarch and salt. Gradually stir in water; blend until smooth. Cook over medium heat until mixture boils, stirring constantly. Remove from heat. Stir about 1/2 cup of hot mixture into egg yolks; return egg mixture to saucepan. Cook until mixture is bubbly. Mixture will be very thick. Remove from heat; stir in 2 Tb Margarine, lemon peel and lemon juice. Pour filling over base.
In small bowl, beat egg whites and cream of tartar at medium speed until soft peaks form, about 1 minute. Add 1/2 cup sugar 1 Tb at a time, beating at high speed until stiff peaks form and sugar is dissolved. Spread meringue over hot filling.
Bake at 350 F for 25 to 30 minutes or until meringue is golden brown. Cool 1 hour. Refrigerate at least 1 hour before serving.