Preheat your oven to 350°F (175°C) and grease and flour a 9x13-inch baking pan.

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

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

Gradually add the dry ingredients to the wet ingredients and stir gently until just combined.

Fold in the diced apples and nuts, making sure they're evenly distributed.

Pour the brownie batter into the prepared baking pan and spread it evenly.

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

Once baked, let the brownies cool in the pan for about 10 minutes.

Transfer to a wire rack, cool completely, then cut into squares to serve.