Preheat oven to 325F (163C).
Except for the walnuts, mix all cookie ingredients until well combined.
Add in the walnuts.
Spoon onto parchment-lined cookie sheet as 4 cookies. Use the back of your spoon to shape, if necessary.
Bake for 8 minutes, and check to see if the cookies are firm. If not, check every 1-2 minutes and remove from oven when firm. Do not overbake!
While cookies cool, begin to make the frosting my mixing the Greek yogurt and whey protein.
Add in Neufchâtel cheese and stevia. Mix well.
Frost cooled cookies, and enjoy! Store in the refrigerator.