Preheat oven to 350º. Spray a 8x8 square pan with cooking spray then line with a strip of parchment paper, leaving an overhang on two sides. Spray paper with cooking spray, too.

In a medium bowl, whisk together flour, cocoa, salt and baking soda.

In another medium bowl, stir together brown sugar, applesauce, greek yogurt, melted chocolate, eggs and oil. Add the flour mixture and stir until just moistened.

Spread batter in prepare pan. Sprinkle the top with the chopped chocolate pieces.

Bake until a toothpick inserted in the center comes out with only a few moist crumbs attached, about 30-35 minutes.