Whisk the vegetable oil and lemon juice until combined.
Add the mustard, soy sauce and finely chopped garlic. Stir.
Add marinade to steak and chill in the fridge for 2 hours.
For a blue steak, cook for 1 minute on both sides on a very hot pan.
For a rare steak, cook for 2 minutes on both sides.
For a medium steak, cook for 3 minutes on both sides.
For a well done steak, 4-6 minutes on both sides.