Combine oats, milk, egg, raisins, and cinnamon in a cereal bowl and mix well.
Microwave on high for up to two minutes. Watch carefully after the first minute and a half. The mixture will rise as it cooks and you want to avoid the mixture overflowing the bowl. The oatmeal is done with the mixture looks cooked and mostly set.
As soon as the oatmeal is out of the microwave, add a dollop of peanut butter and an extra sprinkle of cinnamon if desired.