Preheat oven to 350°F.

Mix together gingersnaps, melted butter, and 1/4 cup granulated sugar until well combined. Press mixture into a 9-inch pie plate, making sure to keep the crust even, using the bottom of a measuring cup or glass to press down.

Bake crust for 10 minutes, then set aside.

In a small saucepan over medium heat, whisk together 1 cup sugar, flour, cornstarch, salt, water, and lemon juice and cook until dissolved.

Beat egg yolks in a small bowl, then slowly whisk in 1/4 cup of the warm sugar mixture to temper the eggs. Once combined, slowly whisk egg mixture into the saucepan and stir in lemon zest.

Reduce heat to medium-low and cook for about 5 minutes, whisking constantly, until mixture is thick and coats the back of a spoon. Pour filling into prepared crust.

In the bowl of a stand mixer, beat egg whites until frothy. Turn mixer to high and pour in remaining 1/3 cup of sugar. Beat until stiff peaks form.

Spoon meringue onto pie filling, spreading to the edges of the crust to prevent shrinkage. Return the pie to the oven and bake for about 10 minutes, until meringue is lightly browned.

Let cool completely before serving.