2) Brush the steak with oil to prevent it sticking to the griddle or pan, and then cook for 3 mins a side plus 1 min each side turned again (this gives you pretty griddle marks) for desirably rare meat; the lemon in the post-hoc marinade 'cooks' it a little more.
3) While the steak is cooking, place the thyme leaves, garlic, oil, lemon zest, juice, salt and pepper in a wide shallow dish.
4) Once the steak is cooked, place it in the dish of marinade for 4 mins a side, before removing it to a board and slicing thinly on the diagonal.