01 - Whisk together soy sauce, mirin, sake, sugar, sesame oil, minced garlic, grated ginger, sesame seeds, and sliced green onion in a mixing bowl until sugar dissolves completely.
02 - Add thinly sliced beef to the marinade, tossing thoroughly to coat each piece. Let stand at room temperature for 10 minutes, or refrigerate up to 1 hour for deeper flavor penetration.
03 - Heat grill pan or tabletop grill over high heat until surface is smoking hot. Ensure proper ventilation as high-heat cooking produces some smoke.
04 - Place marinated beef slices on the hot grill. Cook for 1 to 2 minutes per side until just cooked through and edges develop a slight caramelization. Avoid overcooking to maintain tenderness.
05 - Grill sliced onion, bell pepper, mushrooms, and zucchini alongside the beef until tender with visible char marks, approximately 3 to 5 minutes depending on vegetable thickness.
06 - Arrange grilled beef and vegetables on serving plates. Accompany with steamed white rice while hot for optimal texture and flavor.