Preheat the oven to 350 degrees. Coat a bundt pan with non-stick cooking spray.
Combine the butter, sugar, and 1 teaspoon cinnamon in a microwave safe bowl. Microwave on high heat for 2 minutes, stirring every 30 seconds. Pour into the bundt pan.
Layer the apples and walnuts evenly over the caramel. Set aside.
In a large bowl, combine the cake mix, pudding mix, eggs, oil, water, and the remaining 2 teaspoons of cinnamon. Beat for 2 minutes. Pour over the apple caramel mixture.
Bake for approximately 45 minutes. Begin checking for "doneness" after 30 minutes. A toothpick poked in the center of the cake should come out clean. When cake is done, remove from the oven and cool in pan for 10 minutes.
Carefully invert the cake onto the cooling rack. Allow to cool completely before transferring to a serving plate.