In a large bowl, whisk together the chopped green onions, cilantro, mint, basil, lime juice, soy sauce, red pepper flakes, and honey until combined; set the dressing aside.
Preheat a grill or grill pan to high heat.
Rub the flank steak with olive oil and season both sides with kosher salt and black pepper.
Grill the steak about 5 minutes per side for medium doneness, or until it reaches your desired doneness.
Remove the steak from the grill and let it rest for 5 minutes to retain juices.
Meanwhile, in a large bowl toss together the chopped romaine, baby arugula, and baby spinach until evenly mixed.
Divide the greens among serving bowls and top with the sliced cucumber and halved grape tomatoes.
Slice the rested steak thinly against the grain and arrange the strips over the salads.
Drizzle the cilantro-herb dressing over each salad, toss gently if desired, and serve immediately.