Heat grill to medium-high. Cook the couscous according to the package directions, then fold in the scallions.
In a small bowl, combine the preserves and vinegar. Set aside.
Thread the pork onto eight 6-inch skewers. Rub with 1 teaspoon of the oil and season with ½ teaspoon salt and ¼ teaspoon pepper.
Grill the kebabs, turning often, until cooked through, 10 to 12 minutes. Baste with the apricot glaze during the last 2 minutes of cooking.
In a bowl, toss the plums, the remaining tablespoon of oil, and ¼ teaspoon each salt and pepper. Grill until charred, about 2 minutes per side.
Serve the plums with the kebabs and couscous.