Slice the onion and mushrooms thinly.
Heat olive oil in a pan and sauté the onion.
When the onion becomes translucent, add the mushrooms and continue to sauté.
Add the oatmeal and stir-fry, then pour in 200ml of water or vegetable stock.
Simmer over low heat, stirring, until the oatmeal becomes soft.
Season with salt and pepper.
Transfer to a plate and garnish with parsley.