Drain juice from mandarin oranges and set aside. Make box mix (I use Kroger brand) according to directions but use mandarin orange juice instead of water.
Spray the bottom of your cake pan with butter flavored cooking spray. Place mandarin oranges flat. Add cake mix slowly because the oranges will move. (I use a large spoon and spoon in around edges first)
Bake according to your mix. As soon as the cake is done, turn cake over and leave pan overtop until cooled. Carefully remove the pan.
Get your chocolate frosting (I use Kroger brand in the plastic container) Warm frosting until you can drizzle it over the cake. As frosting is warming, crush your walnuts. As soon as you have drizzled your cake, top with walnuts.