Add the meal replacement shake, peanut butter powder and baking powder to a small bowl and mix until blended.
Whisk the water and egg white together until frothy.
Fold the powdered ingredients into the liquid until blended completely.
Drop batter onto parchment paper lined baking sheet in five even mounds.
Bake at 350 degrees for 7 minutes or until cookies have risen and tops look crackled.
Allow to cool until able to be handled, then enjoy!