Put the red bell pepper in a small casserole.
Cover and microwave on HIGH for 4 minutes.
Rinse the fish fillets and pat dry on kitchen paper.
Season with salt and pepper on both sides.
Place on a board, white side up.
Puree the shrimp (prawns) and chives in a food processor and add salt and pepper.
Spread the fillets on one side with the puree, and roll up, starting with the thick end and ending with the tail.
Drain the red bell pepper and puree.
Put the fish rolls on a round dish.
Cover and microwave on HIGH for 6 minutes.
Pour the red pepper puree into a bowl and add the vinegar, sugar and salt to taste.
Stir well.
Heat for 1 minute on HIGH.
Cut the butter into tiny pieces and beat vigorously into the red pepper puree.