1. Bake pie shell as directed. Cool.
2. In medium saucepan, stir together cornstarch, salt, and ¾ cup Splenda. Add water, stirring until Splenda and cornstarch are dissolved. Cook on medium heat until mixture thickens and comes to a boil, stirring constantly.
3. Beat egg yolks in small bowl. Add about a cup of the cornstarch mixture and stir. Transfer this mixture to cornstarch mixture in saucepan, stirring rapidly. Cook on medium heat until very thick, about 5 minutes.
4. Remove from heat and whisk in margarine and lemon juice. Pour into pie shell.
5. Preheat oven to 400°.
6. In medium bowl, beat egg whites on high speed until foamy. Add cream of tartar and beat until soft peaks form. Add remaining ¼ cup Splenda and beat until stiff peaks form.
7. Spread meringue over pie filling, sealing with crust edge. Bake 10 minutes or until meringue is golden.
8. Remove from oven and cool 1 hour. Refrigerate for 3 hours before serving.

Note: Pie crusts vary from 80 to 150 calories per serving. Read the label to choose one lower in calories. The above calculations were based on a pie crust with 90 calories per 1/8 of a pie.