Mix together egg whites, milk, sweetener, vanilla, cinnamon and salt. Whisk until combined.
Spray a microwave-safe mug with cooking spray. Add enough bread to coat the bottom of the mug. Drizzle with a little of the egg mixture. Add a few more pieces of bread and drizzle with a little egg mixture. Continue to do this until all the bread and egg mixture is used and bread is coated with egg.
Place in microwave and cook for one minute. Check and if still runny at the bottom of mug, cook another 30 seconds. Serve immediately with preferred toppings. Enjoy!