To make the marinade, whisk together all the ingredients.
Place the steak in a Ziploc bag or suitable marinating container and pour over half the marinade. Reserve the rest. Marinade the steak for at least 20 minutes but ideally overnight in the fridge. (Remove the steak from the fridge 1 hour before cooking.)
To cook the steak, heat a grill pan or outdoor grill until hot then cook the steaks for a few minutes per side, to your preference. Remove from the heat and allow to rest for 5 minutes.
Assemble the salad by combining the cucumber, tomato, chilli, spring onion and herbs in a bowl. Slice the steak and add to the salad, pour over the remaining dressing. Toss to combine.