1. Preheat the oven to 375°F. Grease an 11 x 7-inch glass baking dish.
2. Place the flour, butter, milk, vegetable broth, salt and pepper in the bowl fitted with the whisk. Mix at speed 7 for 30 seconds. Launch the sauce program at speed 4 at 190°F for 8 minutes.
3. Place the fish in the prepared dish and put the mussels and shrimp on top. Cover with the sauce and sprinkle with cheese and breadcrumbs.
4. Bake for 15-20 minutes or until the fish flakes easily with a fork.