Place the beef and mushrooms in a food storage bag, add ¾ cup of San-J Korean BBQ Marinade & Stir Fry sauce, coat the beef and mushrooms, and refrigerate for 2 – 24 hours.
Skewer the beef, mushrooms, and scallion pieces onto the skewers. Preheat grill or grill pan to medium-high heat, about 450°F. Warm the remaining ⅓ cup San-J Korean BBQ Marinade & Stir Fry sauce in a saucepan.
Oil the grates of the grill or grill pan. Place the skewers on and let cook undisturbed for 3 minutes. Flip and cook for another 3 minutes for medium-rare beef. Brush with the remining San-J Korean BBQ Marinade & Stir Fry sauce and serve the rest on the side. Top the skewers with sesame seeds.
If desired, serve with nori sheets, cooked rice, and kimchi and everyone can make their own little wraps.