Preheat the oven to 350F and position the oven rack in the middle of the oven. Grease a muffin pan or line it with muffin liners.
Make the batter:
Add the ingredients in the order listed inside the blender jar: the pumpkin puree, Greek yogurt, eggs, oats, protein powder, pumpkin spice, cinnamon, baking powder, baking soda, and salt. Blend, increasing the speed from medium to high speed for about 45 seconds, until the ingredients turn into a smooth batter and you can no longer see oat flakes.
Pour the batter into the 12 prepared muffin pans, filling them no more than ¾ of the way up. Sprinkle the chocolate chips on top of the muffins.
Bake:
Bake the muffins for 22-25 minutes or until a toothpick inserted in the center of a muffin comes out clean.
Remove the pan from the oven and allow the muffins to cool down to room temperature before removing them from the pan.
Serve & store:
You can enjoy these muffins warm or at room temperature.
Refrigerate leftover muffins for up to 5 days or freeze them in a zip bag, for up to 2 months. Reheat for 15 to 30 seconds in the microwave.
Notes
If using plant-based powder, add 2 to 3 tablespoons of water to the batter, as it may be a bit thicker, yielding denser muffins.