Put the broccoli on a microwave safe deep dish big enough to cook the fish on. Salt and pepper the fish fillets and fold in half. Put them on top of the broccoli. Heat the water and stock on full power in the microwave for 1 min. Pour the fish stock over the fish. Cover the dish and cook on full power 5-6 minutes. Pour the broth in a sauce boat and add some water if needed. Mix the flour with a little water. Stir the mixture into the warm sauce. Boil the sauce on full power 3-4 minutes. Stir 3-4 times during this period. Season with lemon juice and heavy cream. Serve the fish with boiled potatoes and the sauce.