In a 1-cup glass measure, whisk pineapple juice, soy sauce, brown sugar, oil, ginger, allspice, chile flakes, and dry mustard to blend. Trim fat on pork chops to 1/4 inch; rinse pork and pat dry. Place chops in a 1-gallon zip-lock plastic bag and add all but 1/4 cup juice mixture. Seal bag and turn to coat. Let stand, turning bag occasionally, at least 20 minutes, or chill up to 1 day (see notes).
Meanwhile, cut pineapple into 1/2-inch-thick slices. Peel onion and cut crosswise into 1/2-inch-thick slices, discarding ends. Place both in a rimmed dish and drizzle evenly with remaining juice mixture. Let stand about 20 minutes, turning slices once.
Lay chops (discard marinade), pineapple, and onion on an oiled grill over a solid bed of hot coals or high heat on a gas grill (you can hold your hand at grill level only 2 to 3 seconds); close lid on gas grill. Cook, turning once, until pineapple and onion are browned, 5 to 6 minutes total, and pork is browned on the outside and no longer pink in the center (cut to test), 5 to 7 minutes total.
Transfer chops to plates. Garnish with grilled pineapple and onion. Sprinkle with mint; offer lime wedges to squeeze over pork.
Wine pairing: Dry Riesling. Try the Trefethen 2003 (Oak Knoll District of Napa Valley; $18), with citrus, apple, and herbal notes.