Preheat oven's griller. Lightly grease a baking dish.
In a large frying pan over medium heat, melt 40g of margarine and saute the spring onions. Toss in prawns and saute until pink, about 5 minutes.
Remove prawns with slotted spoon and set aside. Add cream cheese and milk to frying pan, stirring constantly until cheese melts. Stir in Swiss cheese, wine, cooked prawns and cayenne. Cook until all cheese is melted and prawns are heated through.
Pour mixture into prepared baking dish. Combine bread crumbs and 2 tablespoons of melted margarine, sprinkle over prawns mixture. Grill for 1 to 2 minutes or until golden brown.