In a small bowl, combine lemon juice, spring onion, garlic and wine. Set aside.
Lay fillets flat and divide prawns evenly among them in a band across one end of each fillet. Roll up around prawns and secure with toothpick. Place in a baking dish. Season to taste with salt, pepper and paprika. Pour lemon juice mixture over the fish. Cover.
Bake at 180 degrees C for 25 minutes.
When fillets are nearly done, prepare sauce. In a small saucepan, melt butter over medium heat. Stir in flour. Transfer fish to serving platter and keep warm. Pour pan juices into butter/flour mixture; cook and stir until thickened. Pour over fish and serve.