In a medium pot, heat the oil over medium low heat. (The mixture will bubble a lot so go larger than a saucepan for ease). Add onion and cook until soft and translucent, approximately 5 minutes.
Add the salt, black pepper, ground red pepper, and stir to combine. The amount of salt and pepper may seem like a lot but it will be ok.
Add the Guinness, sugar, and honey. Let the mixture come up to a simmer and reduce heat to medium-low.
You will want to watch this, it froths a lot.
Let the sauce continue to cook and thicken until similar in consistency to honey. This will take ~15 minutes.
Take off stove and put into heat proof measuring cup and let sit at room temperature.
Preheat oven to 400.
Place salmon in baking dish. Cook for approximately 12 minutes for a 1" thick piece of salmon.
If glaze has become too thickened, you can microwave it for a few seconds. Top salmon with Guinness Glaze. Eat immediately!