Heat the oven to 350°F. Coat a 9-inch pie plate with cooking spray.
To make the crust, in a food processor, process the graham crackers until finely ground. Add the butter and water and process until the crumbs clump together. Press the mixture into the bottom of the pie plate and about 1 inch up the sides. Bake for 10 minutes, then let cool.
Meanwhile, make the filling. Put the gelatin in a small bowl; add the boiling water and stir until the gelatin is dissolved. In a medium saucepan, whisk together 1/3 cup of the sugar and the flour. In a medium bowl, lightly beat the milk and egg yolks together. Add the egg-and-milk mixture to the sauucepan and whisk so the flour and sugar dissolve. Cook over medium heat, stirring constantly, until the mixture comes to a boil and has thickened. Stir in the vanilla and dissolved gelatin. Set aside to cool slightly.
Arrange the sliced bananas in the crust and pour the pudding on top. Place in the refrigerator until the pudding has set, about 3 hours.
Whip the cream in a medium bowl with an electric mixer. When it is about halfway to soft peaks, add the remaining 1/2 tsp. sugar, then continue whipping until it barely holds a soft peak. Put the whipped cream in a plastic bag, concentrating it in one corner of the bag. Snip off that corner of the bag and squeeze the whipped cream in a decorative pattern around the pie.
The pie will keep in the refrigerator for 1 to 2 days.