Serve with a bowl of fresh salsa on the side to spoon over the tacos, if you like.
Arrange a rack in the oven about 6 inches from the heating element and preheat broiler. Arrange onion and pineapple on a large foil-lined baking sheet and broil, stirring once or twice, until softened and browned in parts, 6 to 8 minutes; transfer to a platter and keep warm.
Arrange pork on the same baking sheet and broil, stirring once or twice, until cooked through and golden brown, 6 to 8 minutes; transfer to platter with pineapple and onion and toss gently. Spoon onto tortillas, top with cilantro and serve with lime wedges on the side.