In a medium bowl, combine flour, sugar, cinnamon, and salt. Cut in the butter using your fingers or a dough blender to create a crumbly texture. Mix in the cocoa powder and oats. Refrigerate until needed.

Place rack in center of oven and preheat to 350 degrees F. Butter and lightly flour an 8x8 inch or 9x9 inch baking dish.

In a medium bowl, combine flour, baking powder, baking soda, and salt.

In a large bowl, beat together butter and sugar until light and fluffy. Beat in eggs one at a time, then vanilla extract.

Stir in 1/3rd of flour mixture, just until incorporated. Mix in 1/2 cup of the yogurt. Add another 1/3rd of the flour, remaining 1/2 cup of yogurt, then remaining flour mixture.

Pour half of the batter into prepared baking dish. Evenly top with the chocolate hazelnut spread. Microwaving the chocolate hazelnut spread for about 20 seconds makes it easier to distribute. Top with remaining batter. Cover thoroughly with the prepared topping.

Bake in preheated oven until knife inserted in center comes out clean, 60-80 minutes depending on the size of your pan. Allow to cool for 10 minutes before serving.