1Preheat oven to 350 degrees F (175 degrees C). Line 2 baking sheets with parchment paper.
2Beat butter, white sugar, and brown sugar with an electric mixer in a large bowl until smooth. Stir egg white and applesauce into butter mixture until just combined into a dough. Add orange juice with pulp and orange zest to the dough; stir.
3Mix flour, oats, walnuts, baking soda, cream of tartar, and cinnamon in a separate bowl; fold into the dough until evenly incorporated.
4Drop by heaping tablespoon onto prepared baking sheets.
5Bake in preheated oven until bottom of cookies are lightly browned, 10 to 12 minutes. Cool on baking sheets 2 to 3 minutes before moving to wire racks to cool completely.