To make zucchini pickle, toss zucchini with vinegar, sugar, ½ tsp (2 mL) salt and 1 tbsp (15 mL) water. Let stand 30 min. In separate bowl, mix mayonnaise with mustard; set aside.
Meanwhile, rub pork tenderloin with remaining salt and crushed peppercorns. Place on grill preheated to medium-high. Cook 20 to 25 min., or until instant-read thermometer registers 160°F (71°C) when inserted into thickest part of pork. Remove from grill; let rest 10 min.
Meanwhile, grill naan bread 1 to 2 min. per side to lightly toast. Drain and discard liquid from bowl of zucchini pickle. Thinly slice pork. Spread mayonnaise mixture on one side of the 4 naan breads. Top each with sliced pork and zucchini pickle. Fold over naan to enclose filling. Serve with broccoli slaw, if desired.
To crush peppercorns, wrap in pocket of parchment paper and crush with rolling pin.