Heat oil in a medium saucepan over medium heat. Add 1/2 cup onion and couscous; cook 5 minutes, stirring frequently. Add broth; bring to a boil. Cover, reduce heat, and simmer 5 minutes.
Add beans, chipotle chile, and tomatoes; cover and simmer 4 minutes or until the couscous is tender. Serve with green onions and sour cream.