Put steak into a glass bowl. Combine vinegar, apple juice, onion, garlic, sage, pepper, coriander, mustard, salt, and olive oil; pour over steak. Turn to coat with the marinade; cover and refrigerate for 2 hours. Remove steak from marinade and cut into 4 portions. Thread skirt steak, onions, and peppers onto the long skewers, weaving the beef around the vegetables.
Broil 4 inches from heat for 12 to 15 minutes, turning to cook all sides. If desired, boil marinade then use it to baste the skewers as they cook.
Calories per serving: 507
Fat per serving: 27.9g