In a 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 steak into bite-sized pieces and add them to the marinade, ensuring each piece is evenly coated. Let the steak marinate for at least 15 minutes at room temperature or up to 2 hours in the refrigerator for deeper flavor infusion.

While the steak marinates, heat a large skillet over medium-high heat. Once the skillet is hot, add a splash of cooking oil to prevent sticking. Wait for the oil to shimmer slightly.

Carefully add the marinated steak pieces in a single layer to the skillet. Sear the steak bites for 2-3 minutes on each side until a rich, golden-brown glaze develops and the steak is cooked to your desired doneness.

Transfer cooked steak bites to a serving platter. Sprinkle with chopped green onions and sesame seeds. Serve warm.