In a saucepan, combine the sugar, flour, and salt. Add milk in gradually while stirring gently. Cook over medium heat, stirring constantly, until the mixture is bubbly. Keep stirring and cook for about 2 more minutes, and then remove from the burner.
Stir a small quantity of the hot mixture into the beaten egg yolks, and immediately add egg yolk mixture to the rest of the hot mixture. Cook for 2 more minutes; remember to keep stirring. Remove the mixture from the stove, and vanilla. Stir until the whole thing has a smooth consistency.
Clean and rinse berries. If they are large cut in halves or quarters.
Bring water to a boil over medium heat. Add sugar and strawberries and simmer until berries are tender, about 8 minutes. You will still have lumps of berries. If you want a smooth consitency, break the fruit up by pushing the berries with the back of a spoon on the side of the pan.
Dissolve cornstach in a little water and add to fruit, stirring constantly. Add zest if desired.
Bring to rolling boil, stirring constantly. Continue stirring and allow pudding to boil a few minutes. The pudding should no longer be cloudy and regain its shine and gloss.
Repeat steps 4-6 with the blueberries.
Bake frozen pie crust according to a directions on the package.
When shell is cool, dump the three pudding/fruit mixtures into the crust in 3 vertical stripes.
Arrange strawberries on top of strawberry section, blueberries on top of blueberry section, and banana slices on top of vanilla section.