- Mix together the parsley, oregano, garlic, rosemary, chilli, red wine vinegar and a third of the oil. Season with a little salt and pepper then leave to infuse for approximately 2 hours.
- When ready to cook, heat a large griddle pan over a high heat.
- Brush the steak on both sides with the remaining oil, then, when the griddle is smoking hot, carefully put it on to the pan and fry for 4 minutes on each side. Remove the steak, wrap in tin foil and leave to rest.
- Put the sliced mushrooms on to the griddle in a single layer and cook for 2 minutes on each side. Take the mushrooms off the griddle, then add the tomatoes and cook for approximately 2 minutes as well.
- Carve the steak against the grain into long, thin slices and arrange the slices on a serving platter. Drizzle with a generous amount of chimichurri sauce and serve with the mushrooms, tomatoes and watercress.