Instant pot: Saute meat and spices, then onion. 30 minutes on high with lamb and onion, then 15 minutes on high with veggies and prunes. . Spread lamb on a large sheet tray and pat dry. In a small bowl, stir together coriander, cumin, ginger, 2 teaspoons salt, and 1/2 teaspoon pepper, then sprinkle over lamb and toss well to coat.
Heat 2 tablespoons olive oil in a large ovenproof Dutch oven over medium-high heat. Arrange 1/3 of lamb in pot in a single layer and cook, stirring occasionally, until deep golden brown, 6 to 8 minutes. Transfer lamb to a large bowl; set aside. Repeat with rest of lamb, adding 1 tablespoon olive oil for each batch.
Add onions to pot, reduce heat to medium, and cook, stirring often, until softened and golden brown, about 10 minutes. Add tomato paste and cook, stirring constantly, for 2 minutes. Stir in broth, scraping up any browned bits. Return lamb and its accumulated juices to pot. Add 2 cups water, cinnamon, and 1 teaspoon salt; stir well and bring to a boil. Cover pot with lid and cook in oven until lamb is just tender, about 1 1/2 hours.
Uncover pot; stir in chickpeas, dried fruit, and carrots. (Add more water if stew seems dry.) Cover pot; continue to cook until lamb is very tender, about 45 minutes. If desired, uncover pot and cook until thickened, 20 to 25 minutes more. About 15 minutes before serving, prepare couscous following package directions.
Remove stew from oven; discard cinnamon. Season to taste with salt and pepper. Ladle stew over couscous; serve.