Thinly slice the flank steak across the grain and at an angle, creating slices 1 inch wide by 1/4 inch thick.
Whisk together the hoisin sauce, lime juice, honey, garlic, salt, ginger, sesame oil, chile-garlic sauce, red pepper flakes, and black pepper in a bowl; pour into a resealable plastic bag. Add the sliced flank steak, coat with the marinade, squeeze out excess air, and seal the bag. Marinate in the refrigerator for 2 to 12 hours.
Preheat an outdoor grill for medium-high heat, and lightly oil the grate. Remove the flank steak from the marinade, and discard the remaining marinade. Thread the meat onto the skewers.
Cook the skewers on the preheated grill until cooked to your desired degree of doneness, 2 to 3 minutes per side for well done. Garnish with toasted sesame seeds and chopped green onions to serve.
