lemon filling:
Place water, tofu, sugar, cornstarch, oil and salt in a blender.
Process until smooth.
Pour into a 2 qt sauce pan over medium heat.
Bring to a boil, stirring constantly with a wire whisk.
After the mixture thickens reduce heat to low and continue cooking and stirring for 1 minute longer.
Remove from heat and stir in lemon juice and zest.
Pour hot filling into pie crust.
Cover the top of the pie with waxed paper to prevent a skin from forming.
Chill the pie for 8 hours or overnight.
Just before serving, remove the waxed paper.
Spread the top with tofu whipped topping.
You can substitute lime for lemon.
tofu whipped topping:
Place all of the ingredients in the blender and process for several minutes until completely smooth.