Preheat oven to 180°C (350°F) and prepare a muffin mold with muffin liners. Make sure you grease the muffin liners to prevent sticking.
In a large bowl, combine pumpkin puree with egg, almond butter, vanilla extract, cinnamon, a pinch of nutmeg, and a pinch of salt. For sweeter muffins, add maple syrup (see notes*). Stir wet ingredients until smooth.
Sift in protein powder and baking powder, then gently whisk until the mixture forms a smooth batter. Be careful not to overmix. Depending on the type of protein powder used, you may need to adjust the consistency by adding up to 2 tablespoons of milk if the batter is too dry, or a little more protein powder if it’s too wet (see notes*).
Fold through the chocolate chips.
Divide the batter evenly between the muffin cups and top with more chocolate chips, if you desire.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean. Let cool over a baking rack before serving.