Place the tomatoes (and their juices) in a 5- to 6-qt slow cooker and break them up slightly. Add the raisins, cumin, ginger, cinnamon, ½ tsp salt and ¼ tsp pepper and mix to combine.
Add the onion and squash and cook, covered, until squash is tender, 5 to 7 hours on low or 3 to 5 hours on high.
Ten minutes before serving, cook the couscous according to package directions; fold in the cilantro. Gently fold the chickpeas into the stew and cook, covered, until heated through, about 3 minutes. Serve over the couscous.
