Toast walnuts in a large, non-stick pot (without oil) over medium heat, 5 minutes (toasting intensifies their flavour). Transfer to a small bowl.
Heat oil in same pot over medium-high heat. Add onion and cinnamon stick pieces. Stir for 2 minutes, then add sweet potatoes. Pour in broth and bring to a boil. Cover, reduce heat and simmer until sweet potatoes are almost tender, 8 to 10 minutes. Return to boil, add beans and cook until tender-crisp, 5 minutes.
Stir in couscous and raisins, cover, remove from heat and let stand 5 minutes. Fluff with a fork, empty into a serving bowl, and sprinkle with walnuts, parsley and feta.
Per serving: 385 calories, 10 g protein, 8 g fat (2 g saturated fat), 70 g carbohydrates, 10 g fibre, 11 mg cholesterol, 288 mg sodium.