Preheat oven to 325F (163C).
Mix protein powder, coconut flour, baking powder, salt, and 1 tablespoon of erythritol.
Add lemon zest, lemon juice, vanilla, and coconut oil. Mix well. Use your hands to press the dough together.
Separate into 8 pieces, and roll each into a ball. Set on a piece of parchment paper.
Pour 1 tablespoon of erythritol on the parchment (not on the cookies).
Press each cookie into the erythritol, flattening it out. Then place the cookie (erythritol side up) onto a parchment-lined cookie sheet.
Bake for about 13 minutes, or until firm.
Enjoy!