Preheat the oven to 350℃ and prepare an 8x8" baking dish by greasing it or lining it with parchment paper.
In a large bowl, combine the eggs, applesauce, almond butter and vanilla extract and mix well.
Now add the dry ingredients: rolled oats, all purpose flour, brown sugar, cinnamon, baking powder and salt. Stir until it is just combined.
Add the chopped apple and chopped walnuts (optional) to the batter and mix together.
Pour the batter into the prepared baking dish and spread it out using a spatula. Try to make sure it’s evenly distributed throughout the pan for a consistent bake.
Bake for 30-40 minutes, or until an inserted toothpick comes out clean.
Allow the bars to cool for at least 10 minutes before removing the bars from the dish. Slice into 12 or 16 bars or squares and enjoy!