Preheat oven:
Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or grease lightly.
Mix dry ingredients:
In a large bowl, whisk together flour, protein powder, baking soda, baking powder, spices, and salt.
Mix wet ingredients:
In another bowl, whisk together pumpkin puree, eggs, maple syrup, milk, oil, and vanilla extract until smooth.
Combine mixtures:
Pour the wet mixture into the dry ingredients and stir gently until just combined — do not overmix.
Fill muffin tin:
Spoon batter evenly into the 12 muffin cups. Top with chocolate chips or nuts if desired.
Bake:
Bake for 18–22 minutes, or until a toothpick inserted in the center comes out clean.
Cool:
Let muffins cool in the pan for 5 minutes, then transfer to a wire rack to cool completely.