In a large mixing bowl, whisk together soy sauce, brown sugar, honey, minced garlic, grated ginger, sesame oil, and red pepper flakes until well combined.

Cut the sirloin or flank steak into bite-sized pieces, then add it to the marinade. Ensure each piece is well coated. Let it marinate for at least 15 minutes at room temperature, or refrigerate for up to 2 hours.

Place a large skillet over medium-high heat and add a tablespoon of oil. Heat the oil for about 1-2 minutes until shimmering.

Add the marinated steak pieces in a single layer to the hot pan. Sear for 2-3 minutes on one side until caramelized, then flip and sear the other side for another 2-3 minutes.

Transfer the steak bites to a serving platter and sprinkle with chopped green onions and sesame seeds before serving.