Coat a 9x13 inch baking dish with cooking spray and set aside.
In a small bowl, combine the yogurt and baking soda. Set aside.
In a medium bowl, whisk together the flour, baking powder, cocoa powder and salt. Set aside.
In the bowl of an electric mixer, cream the butter and sugar until fluffy. Add the eggs one at a time until thoroughly combined. Add the dry ingredients to the batter alternatively with the yogurt mixture until well combined. Stir in the vanilla.
Pour the batter into the baking dish. Whisk together the nuts, sugar and cinnamon and sprinkle over the top of the cake. Bake for 40 -45 minutes or until a toothpick inserted into the center of the cake comes out clean. Let cool for 20 minutes before serving. Before serving, drizzle the chocolate and caramel topping over the cake. Slice and serve.