Marinate the flank steak in a mixture of fish sauce, lime juice, sugar, and chili flakes for at least 15 minutes.

Grill the marinated beef over medium-high heat for about 3-4 minutes on each side, or until cooked to your desired doneness.

Remove from grill and let it rest for a few minutes before slicing.

In a large mixing bowl, combine the salad greens, cucumber, cherry tomatoes, red bell pepper, and red onion.

Slice the grilled beef thinly and add it to the salad.

Drizzle the dressing over the salad and toss gently to combine.

Garnish with chopped cilantro and crushed peanuts before serving.