Mix the Dry Ingredients: Add protein powder, oats (or oat flour), baking powder, cinnamon, and cocoa powder (if using) into a microwave-safe mug. Stir with a fork until everything is evenly combined.
Add Wet Ingredients: Pour in the milk, Greek yogurt (or mashed banana), and sweetener if desired. Mix until a smooth batter forms. If it looks too thick, add 1 extra teaspoon of milk.
Microwave for 45–60 Seconds: Place the mug in the microwave and heat for 45 seconds. Check the texture. If the center is still wet, continue microwaving in 5 -10 second bursts until cooked but still soft and fluffy.
Rest & Serve: Let the mug cake rest for 1 minute to finish setting. Top with chocolate chips, berries, or a drizzle of honey.