For the steak, heat a griddle pan until smoking. Rub the oil over the steak and season well with salt and freshly ground black pepper. Fry for 3-4 minutes on each side (for rare), or until cooked to your liking, then remove from the pan and allow to rest on a warm plate.
For the chips, parboil the potato in boiling water for 4-5 minutes, then drain and place on a baking sheet. Place the crushed garlic on the baking tray and drizzle over the oil, then bake in the oven for about 12-15 minutes, or until the chips are golden-brown and crisp.
For the mushrooms and onion, heat the oil in an ovenproof frying pan and fry the mushrooms and onion for 3-4 minutes before transferring to the oven to roast for 4-5 minutes.
For the crisp parsley, rub the parsley leaves with the oil and place on a cling film covered plate. Heat in the microwave on high for 30 seconds, then remove to cool.
To serve, pile the chips and garlic onto the serving plate with the steak. Spoon the roasted mushrooms and onions onto the plate, and garnish with the crisp parsley.