Heat olive oil in a large pot over medium heat. Add onion, garlic, fennel, celery, and bell pepper. Cook until softened, about 8 minutes.

Add diced tomatoes, broth, wine, bay leaves, oregano, and red pepper flakes. Bring to a boil, then reduce heat and simmer for 15 minutes.

Add fish chunks and mussels. Cover and cook for 5-7 minutes, or until fish is cooked through and mussels have opened. Discard any unopened mussels.

Stir in parsley, lemon zest, and lemon juice. Season with salt and pepper to taste.

Remove bay leaves before serving.

Serve hot with crusty bread on the side.