Preheat oven to 350 degrees. Spray a muffin tin with non-stick baking spray, coconut oil or line with paper or silicone baking liners. Set aside.
In a mixing bowl, combine the dry ingredients; oats, protein powder, pumpkin pie spice, stevia, baking powder and salt.
In a separate bowl, whisk together the wet ingredients; milk, pumpkin, yogurt, and egg whites. Whisk until smooth and well combine. Gradually add the dry ingredients to the wet ingredients, and mix until combined. The batter will be very thick. Lastly, fold in the chocolate chips. Optional; reserve a couple tablespoons of the chocolate chips to sprinkle on top of the muffins.
Spoon the batter into the prepared muffin tin, filling each cup almost full. These muffins will only rise slightly, so filling a little fuller is okay. Top with the reserved chocolate chips.
Bake the muffins at 350 degrees for 28-30 minutes. Muffins will be golden brown. Remove from oven and let cool for 10 minutes. Transfer muffins to a cooling rack to cool completely. Enjoy right away, or wrap in plastic wrap and freeze.