Preheat oven to 350 degrees F and line a muffin tin with 12 muffin liners.
Measure flour, protein powder, baking powder, salt and cinnamon into the bowl of your stand mixer. Give it a quick whisk until ingredients are combined.
Add pumpkin puree, carrots and eggs and whisk to incorporate.
Add oil and sugar and mix until smooth.
Distribute batter evenly between the 12 muffin cups (about 1/4 cup batter per muffin).
Sprinkle with crushed walnuts and optional chocolate chips over each muffin.
Bake at 350 degrees F for 20-25 minutes, or until toothpick inserted into the center comes out clean.