1. Heat oil in a large Dutch oven over medium heat. Add onion and bell pepper; cook 5 minutes. Add wine and next 6 ingredients; bring to a boil. Reduce heat; simmer 5 minutes, stirring occasionally.
2. Nestle fish into tomato mixture; top with mussels. Cover and cook 8 minutes; gently shake pan twice to stir mussels (do not lift lid). Discard bay leaf and any unopened shells. Sprinkle with parsley.
It's important to scrub each mussel to remove any sand or dirt on the shell. Just hold it under cool running water, and scrub each shell with a stiff-bristled brush, such as a vegetable brush. Then grab the byssal threads (or beard) with your fingers, and pull them out, tugging toward the hinge of the shell.