Preheat your oven, 350 degree.
Prepare plain yellow cake.
Divide it to 2 (almost) equal part in separate bowl.
In one of the bowl add the cocoa powder, dried blueberries and cut nuts, and mix them well.
Grease your "pan" with 1 or 2 teaspoons melted butter or spray. Then pour 2/3 of the sugar cinnamon mix into the "pan", and spread and cover the pan well all over.
Add the melted butter to the yellow mix, and pour all the yellow cake mix into the "pan".
Next pour the cocoa nut cake mix on top of the yellow mix (in center not close to the edge of the pan), because the cocoa nut mix is heavier than yellow mix, it would sink in the yellow cake mix.
With a spoon, go zigzag into the yellow and cocoa cake very softly, just a stroke not more.
Then spread the rest of the sugar cinnamon mixture on top of the cake mix.
Put the "pan" in the preheated oven bake it in 350 degree for 50 minutes to 1 hour, as every one knows check it with toothpick, if nothing stick to the toothpick, the cake is ready, if not, leave it for 10-15 more minutes until is done.
After 10 minutes when the pan is cool turn it over in your plate. You can decorate and design it with any thing you like, whipped cream, icing, chocolate fudge, fruit and Jello (gelatin), mixed nuts....
Because I'm on diet I just ate it plain, as picture, with my hot tea with ginger.