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, ensuring each piece is thoroughly coated. Let stand at room temperature for at least 10 minutes, or up to 1 hour for deeper flavor penetration.
03 - Preheat grill pan or tabletop grill over high heat until smoking hot, approximately 5 minutes. The surface must be sufficiently hot to achieve proper searing and caramelization.
04 - Place marinated beef slices on the hot grill, cooking 1-2 minutes per side until just cooked through with a slight caramelized exterior. Avoid overcooking to maintain tenderness.
05 - Grill sliced onions, bell peppers, shiitake mushrooms, and zucchini alongside the beef until charred at edges and tender-crisp, approximately 3-4 minutes total.
06 - Arrange grilled beef and vegetables on a platter alongside steamed white rice. Serve immediately while hot for optimal texture and flavor.