In a medium skillet, melt one tablespoon of the butter and add the diced apples. Cook for approximately 4-5 minutes until apples get a little soft.
In a medium bowl, mix the oats, flour, baking soda, cinnamon, and salt together.
In a separate large bowl, beat the remaining butter, applesauce, brown sugar and vanilla extract together.
Add in the flour mixture to the wet ingredients, stirring just until just blended.
Fold in the diced cooked apple.
Place in the refrigerator and chill for 10 minutes.
Preheat the oven to 350° F
Line a baking sheet with parchment paper or line with a silicone mat.
Drop the cookie dough onto the baking sheet and flatten slightly.
Bake for 15-18 minutes until golden brown
Cool on the pan for about 2-3 minutes, then transfer to a wire rack to cool completely.