Place the parsley, garlic, chilli flakes, red onion, olive oil, lemon juice and balsamic vinegar in a blender with a mincer attachment. Season with the salt and pepper.
Blend until smooth and pour the sauce in to a bowl.
Oil the steak and season with salt.
Place the steak on a sizzling hot pan and cook for 4-5 minutes.
Turn it over and cook for a further 3-5 minutes.
Remove from the heat and rest for a few minutes.
Place the meat on a plate with fries, season to your liking, slice the meat and spoon over the sauce.