Clean and wash the zucchini, cut them in half lengthwise and slice them. Wash, clean and chop the aubergine. Clean, wash and cut the peppers into strips. Put beans in a sieve, rinse and drain.
Peel the onion and cut into strips. Heat 2 tablespoons of oil in a large pot. Cover the zucchini, aubergine and onion and fry for 2-3 minutes. Clean, wash and chop the tomatoes. Remove vegetables from the pot.
Heat 1 tablespoon of oil in a saucepan and sauté the tomatoes for about 2 minutes. Wash oregano, dab dry and, except for something to garnish, pluck leaves from the stalks and chop coarsely. Deglaze tomatoes with stock and strained tomatoes, puree finely with the chopping stick.
Add steamed vegetables, beans and oregano leaves, simmer for about 2 minutes, season with salt, pepper and sugar. Slice parmesan. Cut caper apples in half. Arrange soup in bowls, garnish with caper apples and remaining oregano and sprinkle with parmesan.