Place the noodles in a large bowl, pour boiling water over to cover and let stand 8 to 10 minutes, stirring occasionally to prevent sticking. The noodles should be soft, but firm. Drain well.

In a small bowl, whisk together the rice wine vinegar, fish sauce, brown sugar, Worcestershire sauce, ketchup, peanut butter, garlic, and red pepper flakes until smooth.

In a large skillet or a wok over medium-high heat, heat the oil. Add the sliced steak and cook, stirring, until cooked through, 4 to 5 minutes.

Add the carrots and cook for 3 minutes. Stir in the bean sprouts, the drained noodles, and the sauce mixture, cooking and stirring until most of the liquid is absorbed, about 5 minutes.

Remove from the heat and stir in the dry-roasted peanuts and scallions. Top with the cilantro, if desired.