Heat a fry pan over medium high heat adding 1 tablespoon of olive oil to the pan.
Season steak well all over with salt and pepper.
Once pan is hot add steak to the pan and cook for 3 minutes on one side.
Turn the steak and cook for three minutes on the other side (both sides should look caramelised).
Remove steak from the pan to a plate, loosely cover with foil and leave to rest until needed.
In the same pan add your sliced portobello mushrooms (this will soak up the meat juices from the steak). Cook for 2 minutes then turn mushrooms.
Add garlic, thyme, a sprinkle of salt and some more olive oil (if mushrooms look dry) and cook for an additional minute so flavours combine, then remove from the heat.
In a serving bowl place balsamic vinegar, 1 tbsp of olive oil and dijon and stir to coat the bottom of the dish.
Add rocket on top of dressing and toss to coat the leaves, then add parsley and gently stir to combine.
Thinly slice the steak and place on top of the rocket along with the mushrooms add any meat or pan juices left over.
Sprinkle with shaved parmesan and enjoy!