Preheat oven to 350°.
Crust
Combine graham cracker crumbs, butter, and 3 tablespoons sugar in a medium bowl; mix well.
Press into a 9-inch pie plate, and bake until lightly browned, about 10 minutes.
Remove from oven, and transfer to a wire rack until completely cooled.
Filling
In a large mixing bowl, beat the egg yolks until they are light yellow. Gradually beat in sweetened condensed milk.
Add lemon juice and beat until smooth. Whisk in Greek Gods yogurt and zest. Pour into cooled pie crust.
Bake 15 minutes. Remove from oven, and transfer to a wire rack until completely cooled. Refrigerate until ready to serve.
Serve topped with whipped cream, optional