Cut the beef into 3-4 cm (1 1/2 in) pieces. Slice the onions and mushrooms. If using carrot and potatoes, cut them into chunks and microwave for a couple of minutes.
Heat the oil in a large frying pan and fry the beef until no longer pink.
Add the onions (and carrot) and fry until soft and translucent, then add the potatoes and mushrooms and stir.
Add the water and bring to a boil. Skim off the foam and simmer over low to medium heat for about 5 minutes, until the vegetables are tender.
Turn off the heat. Break the roux into pieces, add it, and stir until completely melted.
Simmer over low heat for about 5 minutes, stirring occasionally, until thick and glossy. Serve over rice with dried parsley.