Combine steak, apple cider vinegar, garlic, salt and oil in a non-reactive bowl and marinate 3 hours or overnight.
In a medium large saucepan, cover rice with about 1cm cold water, cover with a lid and cook rice 12-15 minutes, until just cooked. Add a little more water if needed and cook another 5 minutes.
To make buttermilk dressing, in a medium bowl or jar with lid, whisk (or shake) together all ingredients until well combined. Add sea salt and freshly ground black pepper to taste.
To cook steak, heat a large frypan over a high heat. Pat steak dry with kitchen paper and drizzle with a little oil to coat. Cook steak on medium-high heat, 2-3 minutes each side, until just done. Let meat rest 5 minutes.
Slice beef against the grain into 5-10mm thick slices, then transfer to a platter to serve. Place the lettuce cups, buttermilk dressing and green sauce in bowls and offer cooked white rice. Wrap beef, rice, green sauce and buttermilk dressing in lettuce cups to eat.
Combine all ingredients in a bowl. Taste and test seasoning, adding a little more salt if needed. Let sit at least 10 minutes, serve on jersey veal lettuce cups or with a simple steak or beef.