Clean and wash the zucchini, cut them in half lengthwise and slice them. Wash, clean and chop the aubergine and tomatoes. Clean, wash and cut the peppers into strips. Put beans in a sieve, rinse and drain.
Peel the onion and cut into strips. Heat the oil in a large pot. Fry zucchini, tomatoes, eggplant and onion covered in it for 2-3 minutes. Wash oregano, dab dry and, except for something to garnish, pluck leaves from the stems and chop coarsely.
Add broth, beans, oregano leaves and tomato paste to the vegetables, 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.