In a medium bowl, whisk together soy sauce, brown sugar, honey, minced garlic, grated ginger, sesame oil, and red pepper flakes. Cut the sirloin steak into bite-sized pieces and add them to the marinade, ensuring all surfaces are well-coated. Allow the steak to marinate for at least 15 minutes at room temperature, or refrigerate for up to 2 hours.

Place a large skillet over medium-high heat. Add a splash of vegetable oil to the hot skillet to prevent the steak bites from sticking. Heat the skillet until the oil shimmers.

Carefully add the marinated steak bites to the pan in a single layer. Sear the steak bites for 2-3 minutes on each side, or until they achieve a rich, golden-brown crust.

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