Preheat the oven to 350 degrees F (175 degrees C). Grease and flour a 13x9-inch pan.

Make cake: Beat cake mix, applesauce, eggs, and oil in a large bowl with an electric mixer at medium speed for 2 minutes. Stir in nuts until combined. Pour into the prepared pan.

Bake in the preheated oven until a toothpick inserted into the center of cake comes out clean, about 40 minutes. Cool in the pan for 15 minutes before inverting onto a cooling rack. Turn cake right-side up and allow to cool completely.

Make frosting: Combine vanilla frosting and cinnamon in a medium bowl; stir until blended.

Spread frosting over cooled cake.