Mix all the ingredients together (apart from the sirloins).
Reserve a small amount (about 1/2 tablespoon) of the marinade for later.
Add the steaks to the marinade, cover and refrigerate for at least half an hour (you can leave them overnight).
Turn on the Optigrill and select the steak setting, then press OK.
Allow the Optigrill to preheat. When it's ready, the indicator light will stop flashing and you will hear a beep.
Cook the steaks on the Optigrill until the desired degree of cooking is reached. Yellow for rare, orange for medium or red for well done.
Remove the steaks from the grill, allow them to rest for a minute or so, then cut into slices.
Drizzle over the remaining marinade.
Serve with whatever you like. We chose boiled rice and a selection of freshly chopped vegetables.