In a small bowl, whisk together the soy sauce, lime juice, fish sauce, brown sugar, sriracha, and minced garlic until well-combined.

Pour the marinade over the flank steak in a resealable plastic bag. Seal the bag and gently massage the marinade into the steak.

Heat a grill pan or skillet over medium-high heat and add vegetable oil.

Grill the marinated steak for about 3–5 minutes on each side for medium-rare.

Let the steak rest on a cutting board for 5 minutes, then slice thinly against the grain.

In a large bowl, combine chopped romaine, halved cherry tomatoes, sliced red onion, cucumber, cilantro, and mint. Toss to mix.

Transfer the salad to a serving platter, arrange the sliced steak on top, and sprinkle with chopped peanuts.

Serve immediately with lime wedges on the side.