Preheat the oven to 350 degrees F (175 degrees C).
Combine flour, baking powder, cinnamon, nutmeg, and salt in a medium bowl. Set aside.
Beat together sugar and shortening in a large bowl with an electric mixer until light and fluffy. Beat in eggs one at a time, mixing well after each addition. Stir in flour mixture until well blended. Fold in walnuts, oats, and apple until combined. Drop spoonfuls of dough 2 inches apart onto ungreased baking sheets.
Bake cookies in the preheated oven until edges are golden, 12 to 15 minutes. Cool on the baking sheets briefly before removing to a wire rack to cool completely.