Preheat oven to 375 degrees. Combine sugar, cinnamon, and salt in a large bowl. Peel and core apples; cut into quarters, then cut crosswise into 1/4-inch pieces. Toss with lemon juice; stir into sugar mixture with walnuts.

Roll out cookie dough, cut out circles, fill with apple filling and shape into hamantashen. 

Bake until golden brown and cooked through, 10 to 15 minutes. Let cool on a wire rack 10 minutes.