In a small bowl, combine Gochujang, Green Onions, Soy Sauce, Rice Vinegar, Garlic, Ginger, Sesame Oil and Brown Sugar. Put half of the mixture in a Gallon resealable bag with the Flank Steak. Marinade for 30 minutes up til overnight. (I highly suggest marinating overnight if you plan ahead)
Put the other half of the sauce in a container and refrigerate until ready to use.
Drizzle the Olive Oil into a cast iron pan, allow pan to heat to a medium temperature. The oil should crackle if you drop some water in the pan. Place the meat in and allow to cook for 5-8 minutes on one side, then flip and allow to cook on the other side for 5-8 minutes. Once you have achieved your desired doneness transfer the meat to a wooden cutting board to rest. This will allow the meat to cook a tad more internally and also will retain more of the juice in the meat.
Add the onion and mushrooms to that same pan. You will want to scrape up any dark bits to add flavor to the rest of the dish. Cook for about 10 minutes until the onions and mushrooms are soft.
Add the ramen noodles, water and Peanut Butter Powder. Simmer until the ramen noodles are cooked, about 7 minutes.
Slice the meat, thinly, across the grain.
Your meat should still be hot but if it has cooled you can add it to the pan for a few moments to heat it up.
Put the noodles in a large bowl, place a few slices of steak on top. Garnish with green onion and lime if desired. ENJOY! :D