Heat oven to 350′ F. In a food processor, process the gingersnaps until fine crumbs form.
Add the butter, granulated sugar, and 1/2 teaspoon of the salt and pulse until moistened.
Press the mixture firmly into the bottom and up the sides of a 9-inch pie plate using a straight-sided dry measuring cup to help.
Place on a rimmed baking sheet and bake until the edges are dry and set, 16 to 18 minutes.
(Note: The bottom will still appear moist and soft but will become firmer as it cools; this a crunchy cookie crust, not a soft graham cracker-style. Let cool.
In a medium bowl, whisk together the eggs, condensed milk, lemon zest and juice, and the remaining 1/2 teaspoon of salt.
Pour the mixture into the crust and bake until set in the center, 18-20 minutes.
Let cool and then refrigerate until firm, at least 2 hours.
Using an electric mixer, whip one cream and confectioners sugar on medium until soft peaks form,
2-3 minutes Spread on the pie, sprinkle with the additional zest, and serve immediately.