Make sure the prawns are completely defrosted then put in a bowl and cover with the lime juice and a couple of splashes of tabasco. Set aside for 10-15 minutes.
Preheat grill to hot. Heat the olive oil in a saute pan and add the red onion and garlic. Gently cook for about 3 minutes before adding the chillies. Continue to cook for a couple of minutes more.
Divide the onion mixture between two gratin dishes. Drain the prawns and divide these equally too. Season well then pour over the cream.
Sprinkle the mozzarella on top then place under the grill for about 10 minutes until the cheese is bubbling and brown and the prawns are pink.
Serve scattered with the coriander and fresh french bread to mop up the juices.