Thinly slice the ribeye or sirloin steak against the grain. In a mixing bowl, combine soy sauce, brown sugar, sesame oil, minced garlic, grated ginger, and chopped scallions. Add the beef slices to the marinade, ensuring every piece is well-coated. Marinate for at least 30 minutes or up to 2 hours in the refrigerator for deeper flavor.

Heat a large skillet or a grill pan over medium-high heat for about 5 minutes, making sure it's hot enough to sear the beef quickly.

Once ready, add a splash of oil to prevent sticking. Lay the marinated beef slices in a single layer and cook for about 2-3 minutes on each side until browned and caramelized. Transfer to a plate and continue with the remaining batches.

Once all beef is cooked, serve on a large platter. Garnish with additional chopped scallions or sesame seeds if desired. Serve over cooked rice or in lettuce wraps.

Gather family or friends to enjoy this delightful meal. Pair with pickled vegetables for a tangy contrast.