Preheat your oven to 350°F (175°C) and grease and flour a 9x13-inch baking pan or line it with parchment paper.

In a large mixing bowl, combine the applesauce, brown sugar, granulated sugar, vegetable oil, eggs, and vanilla extract. Whisk until smooth and glossy.

In another bowl, whisk together the all-purpose flour, cocoa powder, baking soda, salt, and ground cinnamon.

Gradually add the dry mixture to the wet ingredients, stirring gently until just combined.

Fold in the diced apples and chopped nuts, ensuring even distribution.

Pour the batter into the prepared baking pan, spreading it evenly.

Bake for 25-30 minutes, checking doneness with a toothpick.

Allow the brownies to cool for about 10 minutes in the pan, then transfer to a wire rack to cool completely.

Once cool, cut the brownies into squares and serve.