Preheat the oven to 375 °F. Lightly spray a 9x13-inch casserole dish with nonstick spray.
Whisk together the applesauce and ½ cup of the honey (save ¼ cup of honey for topping)
Whisk in the egg and egg whites
Whisk in the baking powder, salt, cinnamon and vanilla extract
Stir in the milk
Stir in the oats
Stir in ½ cup chopped walnuts
Pour the mixture into the prepared casserole dish and top with another ½ cup chopped walnuts.
Bake for about 45 minutes. It's done when the oatmeal starts to turn golden brown at the edges. A skewer or knife inserted into the center of the oatmeal should come out clean.
When the oatmeal is still hot out of the oven, drizzle with the remaining ¼ cup of honey.