1) Whisk together soy sauce, gojuchang, rice vinegar, lime juice, and honey in a large bowl. Add flank steak and coat well. Let marinate for at least 30 minutes or you can make well in advance.
2) Two ways to cook flank steak:
– On Grill, cook over medium-high heat for 5-6 minutes per side. As the flank steak cooks, spoon over extra marinade to create a glaze on the steak. Cook until steak reaches an internal temp of at least 135-140 degrees F. in the thickest part of the steak. Remove, cover with foil, and let rest for 10 minutes before slicing against the grain.
– In a skillet, preheat oven 350 degrees F. Add steak to a large cast iron skillet over medium-high heat. Cook for 4 minutes per side to get a nice sear on the steak. Spoon extra marinade over the steak and put it in the oven to finish cooking. Roast for 5 minutes. Check temperature. It should reach 140 degrees F. in the thickest part of the steak. Might need an extra minute or two in the oven depending on thickness of the steak. Remove, cover with foil and let rest for 10 minutes before slicing against the grain.
3) Stir together spicy mayo and make crunchy veggie salad.
4) Make sandwiches by smearing on some spicy mayo and adding a bed of crunchy veggies. Top with a few slices of steak (or chop the steak depending on the texture you like). Add sesame seeds if you want and serve!