Clean and wash the zucchinis and cut them in half lengthwise. Hollow out the zucchini with a teaspoon. Chop the flesh finely. Peel and finely chop the onion. Clean, wash and chop the soup greens into small cubes.
Heat the oil in a pot. Fry the rice, onions, chopped courgettes and soup vegetables. Add 3/8 litres of stock, bring to the boil, cover and allow to swell for 20 minutes over a low heat. Fill the zucchinis with the risotto.
Place in an ovenproof casserole dish, add the remaining stock, cover and cook in the preheated oven (electric range: 200 °C/ gas: level 3) for 15 minutes. Wash the chervil. Put something aside for garnishing.
Finely chop the rest. Stir sour cream with cornstarch until smooth. Remove the zucchinis from the tin and keep warm. Pour stock into a pot, stir in sour cream and bring to the boil. Season to taste with salt and pepper.
Stir in the chervil. Put the zucchinis back into the mould. Serve with the sauce. Garnish with chervil.