Grill or pan-sear the steak until cooked to your desired doneness. Let rest for 5 minutes, then slice thinly against the grain.
In a large bowl, whisk together the fish sauce, lime juice, brown sugar, and chili-garlic sauce.
Add the sliced steak, red onion, cabbage, romaine, cucumber, cilantro, and mint. Toss to coat.
Top with the chopped peanuts and serve immediately.
