Place Guinness and brown sugar in a saucepan and bring to a boil over high heat. Lower heat to medium-high and reduce the liquid by half. This will take about 20 minutes and you will end up with approximately 1/2 cup of syrup.
In a separate saucepan, bring the three cups of water to a boil and slowly stir in the oats and add the pinch of salt. Reduce to a simmer and cook for 25-30 minutes. This mixture will need to be stirred frequently to prevent burning on the bottom. This recipe will yield 2 generous portions of oatmeal or 4 smaller ones.
Since there is a lot of stirring and cooking over a 30 minute period of time, I suggest you tuck into a nice hot cup of coffee. Feel free to add whatever type of "fortification" you desire to you mug. Once the liquid has sufficiently reduced, it will lightly coat the back of a spoon. The mixture may still appear a bit thin to you at this point, but will continue to set up and thicken as it cools.
When oatmeal is cooked to your liking, place in a bowl and drizzle with the Guinness syrup.