Preheat oven to 350°
In a medium mixing bowl, whisk flour, baking soda, cinnamon and salt together. Set aside.
In a large mixing bowl, beat softened butter, brown sugar and sugar together until creamy.
Add eggs and vanilla, then beat until combined.
Stir flour mixture into sugar mixture and mix until incorporated.
Stir oatmeal, chopped apples and walnuts together then add to the mixture. Stir.
Using a 1 inch cookie baller (or rounded tablespoon) drop onto an ungreased baking sheet.
Bake for 12 minutes then remove from oven and let sit for a couple minutes then transfer to wire rack to cool.
Mix powdered sugar and milk together.
Drizzle over cookies that have cooled completely.
Recipe adapted from Quaker Oats.