Spray a (microwavable) mug or small bowl with non-stick cooking spray.
Combine all ingredients in mug and microwave for 30 seconds, stir and microwave for 1 minute, stir around batter again and microwave once more for 30 seconds. If cake still appears wet, microwave for about 15-30 more seconds.
Enjoy straight from your mug or transfer to a small plate and top with fresh fruit, Greek yogurt, whipped topping