Combine marinade ingredients in a bowl and add flank steak. Turn to coat and set aside for 15 minutes.
Heat 1 Tbsp vegetable oil in a large skillet over MED HIGH heat. Remove excess marinade from steak and cook in a single layer for 2-3 minutes, stirring to cook both sides. Depending on the size of your pan, you might need to cook the beef in batches. Remove steak to plate.
Heat remaining 1 Tbsp vegetable oil in skillet, then add peas, carrots and green onion and cook, stirring often, for 2-3 minutes.
Whisk together broth, soy sauce, brown sugar, rice vinegar, garlic, sesame oil, fresh ginger, cornstarch and red pepper flakes. Add steak and sauce to skillet, stirring to combine. Sauce will thicken.
Stir in cooked ramen noodles, if using, and serve!