Preheat the broiler. Rub the olive oil over the flank steak and season with the salt and pepper. Place the steak under the broiler and cook until browned, 6 to 7 minutes per side. Remove from the broiler, cover with foil, and set aside.
In a small bowl, whisk together the soy sauce, lime juice, sesame oil, ginger, fish sauce, and jalapeño. In a large bowl, combine the basil, cilantro, cucumber, onion, and bean sprouts and toss well with the soy dressing. Arrange the noodles on top.
Slice the steak into 1/4-inch pieces, cutting against the grain, and place over the noodles. Garnish with additional basil and cilantro, if desired. Serve.
To make up to 1 day ahead, prepare and store separately in the refrigerator: steak, dressing, vegetables, and noodles. Assemble up to 3 hours before serving.