In a slow cooker, stir together the soy sauce and brown sugar. Add the scallions, garlic and ginger; season with pepper. Add the ribs and toss to coat. Add 1 cup water and cook on low heat until the meat is tender, 5 to 5 1/2 hours.
In a bowl, pour the boiling water over the couscous; season. Cover and let stand for 10 minutes; fluff.
Meanwhile, using tongs, transfer the ribs to a platter. Pour the sauce from the slow cooker into a large saucepan; skim off and discard the fat. Bring to a boil, add the bok choy and cook until the stems are crisp-tender, 4 to 5 minutes. Transfer to the platter. Serve the ribs with the bok choy and couscous; serve extra sauce on the side.