Prepare filling by melting the butter 1 minute at HIGH, stir in the flour; add the milk or cream, salt and pepper to taste.
Microwave 2 minutes at HIGH.
Stir until creamy.
Add the mushrooms and the shrimp.
Microwave 1 minute at HIGH.
Cover the bottom of a dish with half the fillets, pour the shrimp mixture on top.
Cover mixture with the rest of the fillets.
Mix the breadcrumbs with the melted butter and the paprika, scatter over the fillets.
Microwave 10 minutes at HIGH.
Garnish with little bunches of watercress before serving.