In a medium-sized mixing bowl, combine hoisin sauce, sherry, soy sauce, barbecue sauce, green onions, garlic, and ginger. Whisk thoroughly to ensure all ingredients are well blended into a smooth marinade.

Place the thinly sliced flank steak into a resealable plastic bag or a shallow dish. Pour the prepared marinade over the beef, ensuring all slices are evenly coated. Seal the bag or cover the dish with plastic wrap, and refrigerate for a minimum of 2 hours, or ideally overnight, to allow the flavors to fully infuse.

When ready to cook, preheat an outdoor grill to high heat or a stovetop grill pan to medium-high heat. Lightly oil the grill grates or pan to prevent the beef from sticking.

Remove the marinated beef slices from the refrigerator. Thread the slices onto the skewers, leaving a small gap between each piece to ensure even cooking. Discard any excess marinade.

Place the assembled skewers on the preheated grill and cook for approximately 3 minutes per side, or until the beef is slightly charred and cooked to your desired level of doneness. Monitor closely to avoid overcooking.

Remove the skewers from the grill and serve hot. Pair with steamed rice, a crisp green salad, or a flavorful dipping sauce for a complete and satisfying meal.