Heat oil in large saucepan on medium heat. Add onion and garlic; cook and stir 5 minutes or until tender. Add cumin, cinnamon and cayenne pepper; cook and stir 1 minute.
Stir in tomatoes, stock, salt and saffron. Bring to boil. Add shrimp, scallops and mussels. Return to boil. Reduce heat to low; cover and simmer 5 minutes or until mussel shells open; (Discard any that do not open.) Serve with cooked couscous, if desired