Preheat the oven to 350℉. Line an 8x8 or 9x9 square baking dish with parchment paper and grease with non-stick cooking spray.
Whisk together the dry ingredients in a medium bowl: flour, oats, baking soda, and salt. Set aside. Combine wet ingredients in a large bowl: butter, egg, brown sugar, and applesauce. Add dry ingredients into the wet ingredients. Mix only until combined
Fold in the chocolate chunks.
Spread the batter into the prepared baking dish. Bake for approximately 30 minutes.
Once the edges start to brown, remove from the oven and let cool on a rack for 15 minutes.
Carefully lift the parchment and bars from the pan and allow to fully cool on the wire rack.