In a medium bowl, combine ¼ cup soy sauce, 2 tablespoons sesame oil, 2 minced garlic cloves, 1 tablespoon freshly grated ginger, 2 tablespoons brown sugar, and a pinch of black pepper. Whisk until the sugar dissolves and well blended.

Place steak in a resealable plastic bag or shallow dish. Pour the marinade over and coat well. Seal or cover and refrigerate for at least 1 hour, preferably overnight.

Wash and chop mixed vegetables into bite-sized pieces. Set aside.

Preheat your grill to medium-high heat, around 400°F (200°C). Add 1 tablespoon of vegetable oil to the grates to prevent sticking.

Remove marinated steak from the fridge, let excess marinade drip off, and grill for about 3-5 minutes on each side until internal temperature reaches 135°F (57°C).

Transfer grilled steak to a plate and let rest for 5 minutes to redistribute juices.

Add another tablespoon of vegetable oil and grill vegetables over medium-high heat for about 4-5 minutes until tender-crisp.

Slice the rested steak against the grain into thin strips and arrange on a platter with grilled vegetables.

Drizzle any remaining marinade over the platter. Serve with a side of steamed rice or soba noodles if desired.

Sprinkle chopped green onions and sesame seeds over the steak and vegetables before serving.