Whisk together the almond flour, protein powder, baking powder, cinnamon, nutmeg, and salt in a medium bowl. In a separate bowl, whisk together the coconut oil, egg, and vanilla. Stir in the avocado until no large lumps remain. Stir in the honey and (optional) liquid stevia. Alternate between adding the almond flour mixture and milk, beginning and ending with the flour mixture, and stirring just until incorporated. (For best results, add the flour mixture in 3 equal parts.) Let the batter rest for 10 minutes. Gently fold in the carrots.