Defrost the prawns if necessary. Wash and peel the asparagus and cut off the woody ends. Cut asparagus into large pieces. Clean, wash and dice the peppers. Peel and finely dice onion and garlic.
Heat 1 tablespoon of oil in an ovenproof pan. Sauté the bell pepper, onion and garlic in it. Add the tomatoes and juice and chop a little. Season with salt, pepper and sugar. Bring to the boil and simmer for about 20 minutes.
Cook the asparagus in boiling salted water with 1 teaspoon sugar for about 12 minutes. Drain.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Wash parsley, shake dry and chop finely. Mix sauce, asparagus and parsley and fill into a gratin dish. Crumble feta over it.
Bake in a hot oven for 12-15 minutes.
Wash the prawns, dab dry. Heat 1 tablespoon of oil in a frying pan. Fry the prawns in it all around for about 3 minutes. Season with salt and pepper. Take asparagus out of the oven and spread prawns on top.
Baguette goes well with this - at 2 slices per person you will still stay under 400 kcal.