Cut the tops off the tomatoes and scoop out the flesh with a teaspoon. Reserve the "lids" and finely chop the flesh. Halve the courgettes, scoop the flesh out with a teaspoon and cut into four equal pieces. Again, finely chop the flesh. Cut the stalks off the mushrooms and chop finely.
Finely chop the garlic, onions, pepper and parsley. Dice the carrots. Put the finely chopped tomato flesh, the vegetables, garlic, onions, pepper and carrot in a bowl and mix well.
Quickly brown the couscous in a pan with some olive oil, add 300 ml vegetable stock and leave to stand, covered, for about 10 minutes as indicated on the packet. Carefully mix the couscous, vegetables and other ingredients and season with plenty of salt and pepper.
Preheat the oven to about 200 °C. Fill the tomato, courgette and mushroom shells with the mixture and put in a casserole. Add the rest of the vegetable stock and cook on the middle shelf of the oven for about 20-30 minutes. Just before serving, replace the lids on the tomatoes.
Tip: If you wish, you can sprinkle cheese on the stuffed vegetables 5 minutes before the end of the cooking time.