Mash up the banana, and then mix it with all of the cake ingredients in a large mug.
Cook in the microwave, on high, for 1-3 minutes. I usually set for 1.5 minutes, and then finish it in 30-second increments until it’s mostly done, which for my microwave and mug takes about 2 minutes.
When it’s done, you can add the topping and eat straight from the mug, or pop it out onto a plate and add the toppings. For the toppings, I just put them on top while the cake is still warm, so it melts. Enjoy!