In a 12 oz. mug, whisk together flour, protein powder, cocoa powder, baking powder, and salt. Add non-dairy milk, maple syrup, melted coconut oil, and peppermint extract. Whisk to combine until a smooth batter forms.
Microwave on high for 90 seconds until top is matte and slightly firm to touch. Cooking time may be more or less depending on the power of your microwave.