Place the beef in a bowl, and pour in the cooking wine, pear juice and black pepper. Stir to combine, and allow to marinate for 30 minutes. Stir in the soy sauce, sugar, sesame oil, garlic, spring onion and sesame seeds, and marinate in refrigerator at least 2 hours or overnight.
Preheat an outdoor BBQ for medium-high heat.
Remove the beef from the marinade, and discard the marinade. Place a sheet of aluminium foil on the heated barbecue, and lay the beef slices separately on the foil. Place the mushrooms and onion on another part of the foil. Cook the beef slices until they are evenly brown, 3 to 5 minutes per side. Serve with cooked mushrooms and onion.