Combine the garlic, coriander, cayenne, lime and pinch of salt with enough olive oil to make a loose paste. Coat the flank steak, cover with plastic wrap and let marinate up to 2 hours at room temperature or overnight in the refrigerator.
Preheat the grill.
Grill the peppers on all sides until they are BLACK! Remove them from the grill and place them in a bowl covered with plastic wrap. Let them sit for 15 to 20 minutes, remove the plastic and let the peppers cool. Remove all of the black char, stems and seeds. Cut the peppers into 1/2-inch strips and reserve.
Remove the steak from the marinade. Place on preheated grill and cook to desired doneness, about 6 to 7 minutes on each side for medium-rare. Remove from the grill to a cutting board and let rest for 10 to 15 minutes before slicing.
While the steak is grilling, toss the zucchini and onions with olive oil and salt. Grill the zucchini and onions on both sides until they are charred and soft, about 4 to 5 minutes on each side. Remove from the grill and reserve.
To assemble the sandwich:
Slice the flank steak very thin on the bias, make very wide, very thin slices. Cut on a severe angle.
In a large bowl, toss the arugula with the Parmigiano and the peppers and dress generously with balsamic, olive oil and salt. Cut 1 edge off the pita and carefully open it. Lay the arugula, Parmigiano and pepper mixture in the pita, followed by the steak and a layer of zucchini and onions. Close the pita and give a little press to secure. Repeat with remaining pitas. Serve right away or wrap in aluminum foil to take with you for lunch. Oh baby...what a pita!