Preheat oven to 350°F.
In a small bowl, whisk together flour, baking soda and salt. In a stand mixer fitted with the paddle attachment, cream butter and sugars until light and fluffy. Slowly add egg and continue mixing. Slowly add flour mixture, oats, peaches, walnuts and white chocolate chips. Mix until combined.
Line 2 sheet trays with parchment. With wet hands, make 20 balls from the dough placing evenly among sheet trays. Press down on cookie dough with palm of your hand to make a flat circle.
Bake for 10 to 12 minutes or until golden and still a bit tender in the center. Remove from oven and let sit on the sheet trays for 1 minute. Remove cool completely to cooling racks.