Heat an outdoor grill or a grill pan over medium-high. Season the chops on both sides with salt and pepper. In a shallow dish, combine about 4 tbsp. EVOO, 2 tbsp. vinegar, the rosemary, Worcestershire sauce and garlic. Add the chops and turn to coat.
In a medium bowl, combine the remaining 2 tbsp. EVOO, 1 tbsp. vinegar and the sugar. Toss the dressing with the plums, onion, basil and mint; season.
Grill the chops, turning once, until an instant-read thermometer inserted into the center registers 145 degrees , about 10 minutes. Divide the chops among plates; top with the plum sauce.