This is a nice small side dish, or a swell topping for steak, hamburgers or hot dogs. It's worth making just for the aroma.
Heat the olive oil or butter in a large frying pan over low-medium heat. Add onion and pepper pieces and saute until the onions are barely beginning to soften and become translucent.
Increase the heat to medium-high and add the mushrooms. Cook, stirring frequently. The mushrooms will make a kind of squeaky-clean noise as you stir the mixture. Eventually, sweat will appear on the mushrooms' surface, but it won't accumulate in the pan. Stop cooking when the mushrooms are just tender. Add salt, pepper, hot pepper sauce and optional MSG, stir well and serve.
Serves 4 as a side dish.