In a large skillet, saute onion in oil until tender. Add the beans, sweet potatoes, broth, chipotle, pepper and cinnamon., Bring to a boil. Reduce heat; cover and simmer for 25 minutes. Uncover and simmer 5-10 minutes longer or until potatoes are very tender and mixture is thickened, stirring occasionally., Meanwhile, cook couscous according to package directions. Serve with black bean mixture.