Prepare the beef: Slice the flank steak or sirloin against the grain into thin strips. The thinner the slices, the more tender and flavorful each bite will be. If the beef is slightly frozen, it’s easier to cut evenly.

Make the marinade: In a mixing bowl, combine soy sauce, sesame oil, gochujang, brown sugar, garlic, and rice vinegar. Stir everything together until the sugar dissolves completely. The marinade should be a perfect balance of sweet, savory, and slightly spicy.

Marinate the beef: Add the sliced beef into the marinade and toss to coat. Cover the bowl and let it marinate in the fridge for at least 30 minutes. If you have more time, marinate for 1-2 hours to enhance the flavors.

Cook the beef:

Stovetop method: Heat a large skillet or wok over medium-high heat. Add a small amount of sesame oil. Once the pan is hot, add the marinated beef in batches, making sure not to overcrowd the pan. Cook for 2-3 minutes, stirring occasionally, until the beef is browned and cooked through.

Grill method: Preheat your grill to medium-high heat. Grill the beef for about 2-3 minutes per side, ensuring it’s slightly charred and perfectly tender.

Garnish and serve: Once cooked, transfer the beef to a serving plate. Sprinkle with sesame seeds and chopped green onions for an extra burst of flavor and crunch.