Combine the water and sugar in a small saucepan and heat to a simmer. Stir in the julienned lime zest and simmer for 30 minutes. Strain and reserve 1/3 cup of the syrup. Discard the rest.
Preheat the oven to 375°F.
Prepare the crust:
Combine the graham crackers, brown sugar, grated lime zest, and butter in a food processor and process until the mixture holds together. Press into the bottom and sides of a 9 inch pie plate and bake for 8 minutes. Set the crust on a wire rack to cool.
Prepare the filling:
Heat the reserved syrup in a small saucepan. Remove the pan from the heat and sprinkle the gelatin over the syrup. Let it soften for 1 minute. Stir in the lime juice, 1/4 cup of the sugar, and the 2 egg yolks. Stir over low heat until the mixture is thick and frothy (5 minutes). Set aside to cool to room temperature.
Beat the egg whites and 2 Tbs of the sugar with an electric mixer until stiff. Transfer the whites to a large bowl.
In another bowl, whip the cream, vanilla, and 2 Tbs sugar with the mixer until it is thick. Fold the whipped cream into the egg whites while drizzling with the reserved lime mixture. When the mixture is smooth, spoon it into the prepared crust.
Chill, uncovered, until firm (2 to 3 hours).
Optional: Top with additional whipped cream and a slice of lime.