Preheat oven to 350 degrees fahrenheit and line a baking sheet with parchment paper or a silicone baking mat.
Mix grated apple, peanut butter, milk, melted butter and vanilla extract until well combined.
In separate bowl mix whole wheat flour and oatmeal then slowly add to wet mix, stirring until all ingredients are mixed.
Roll into 1 inch balls and place on greased baking sheet. Flatten each ball with a fork, making a criss-cross pattern.
Bake for 10 minutes or until cookies begin to brown.
For a crunchy treat turn off the oven and allow treat to remain in oven while it cools.
Cool and refrigerate.