For the marinade, in a medium bowl, whisk together passion fruit juice, 2 tablespoons of the scallions, the soy sauce, oil, ginger, cumin, coriander, and ½ teaspoon of the pepper; set aside.
For the drizzle, in a small bowl, whisk together lemon juice, lime juice, salt and the remaining ¼ teaspoon pepper, whisking until salt is dissolved. Cover and chill until serving time.
Slice meat across the grain into thin slices. Place meat in a resealable plastic bag. Pour marinade over meat; seal bag, turning to coat meat. Place in a shallow dish. Cover and marinate in the refrigerator 1 to 2 hours.
Thread meat slices accordion-style onto twelve 12-inch skewers (see Tip), adding sweet peppers with meat. Lightly coat grill rack with cooking spray.
For a charcoal or gas grill, grill skewers on prepared rack of a covered grill directly over medium-high heat about 4 minutes or until meat is desired doneness, turning once halfway through grilling time. Transfer to a serving platter. Drizzle with the lemon-lime mixture. Sprinkle with the remaining 2 tablespoons scallions.
Tips: For easier cutting, freeze flank steak 30 to 60 minutes before slicing.
If using wooden skewers, soak in enough water to cover for 30 minutes; drain before using.