Line a large rimmed baking sheet with parchment. If your baking sheet is smaller than 13x18 inches, use two sheets or cut the recipe in half. Preheat the oven to 325 degrees F.

With an electric mixer, beat the egg whites until soft and foamy (not stiff). Add the cake mix, oil, water, milk powder vanilla and oats and stir until you have a very soft dough. Stir in the chips and nuts.

Dampen fingers and press the dough into a large slab about 12x14 inches. It should be very thin.

Bake for 20 minutes. Remove from the oven and score with a pizza cutter. Separate the pieces just a little bit. Turn off the oven and put the tray back inside. Allow the bark to sit in the "off oven" with the door closed for another 5 minutes. Note: If your bark is very brown around the edges, you can skip putting it back in the oven and just let it cool on the sheet.