Heat the oven to 400 F. Cook the couscous according to the package directions. Meanwhile, heat the oil in a large ovenproof skillet over medium-high heat. Season the pork with 1⁄2 teaspoon salt and 1⁄4 teaspoon pepper and cook until browned, 3 to 5 minutes per side. Transfer to a plate.

Add the peaches, onion, vinegar, and 1⁄4 teaspoon each salt and pepper to the skillet, and cook, tossing, for 1 minute. Return the pork and any accumulated juices to the skillet.

Transfer the skillet to the oven and roast until the pork is cooked through and the peaches are tender, 8 to 10 minutes. Serve with the couscous and sprinkle with the basil.