Whisk egg white in a separate cup, add remaining wet ingredients, whisk to mix well. If your applesauce is thick, dilute with a bit of water before using.
Add to dry ingredients. Mix well.
Microwave 3 minutes on high. (1000W). The cake will likely rise above the top of the cup but that's OK.
Let stand 1 - 2 minutes to finish rising and cool slightly.
Run a knife around inside of cup, tip out and eat.
If you diet allows it, this is nice with a bit of vanilla ice cream. Otherwise try it with some diet whipped topping.