In a 12-oz microwave-safe mug, whisk together flour, sugar, baking powder, and salt with a fork until well combined.
In a separate small bowl, beat one egg. Measure out half (about 2 tbsp) and save the remainder for another use.
Add the measured egg, strawberry Greek yogurt, oil, and vanilla extract to the mug. Mix thoroughly until the batter is smooth with no dry spots.
Fold in the diced strawberries.
Gently tap the mug on the counter a few times to remove air bubbles.
Microwave on high for 1 minute 45 seconds to 2 minutes, or until the cake is set but still slightly moist on top. Cooking time may vary depending on your microwave's power.
While the cake cools slightly, whip the heavy cream with powdered sugar until soft peaks form.
Top the warm cake with whipped cream, sliced strawberries, and a mint leaf if desired.