Preheat oven to 350F, and spray a mini bundt pan with nonstick spray {I'm partial to the baking kind with flour inside!}.

In a large bowl, whisk together the egg whites, pumpkin puree, and sugar until combined. Mix in the vanilla extract and yogurt, and mix.

Add in the flour, baking powder, baking soda, salt, and pumpkin spice mix, and mix everything well. Finally, stir in the chocolate chips.

Divide batter evenly in the pan, being sure to not fill each cavity more than ⅔ - ¾ of the way.

Bake 15-28 minutes, until the cake is spongy to the touch, and a toothpick inserted in the center comes out with just a couple of moist crumbs

Let cool slightly, then remove from pan and sprinkle with powdered sugar.