Combine the flour (or instant oats) with the protein powder, baking powder, and water. Microwave the mixture for about 2 minutes.
In a separate bowl, mix the cocoa powder with a splash of water. Optionally, sweeten the cocoa mixture and the Greek yogurt with flavor drops or flavor powder.
Top the mug cake with the Greek yogurt and cocoa mixture. Refrigerate overnight. In the morning, you can add an Oreo if you like.
