Clean, wash and roughly dice the peppers. Peel and dice the onion. Heat olive oil in a pot and fry the onion in it. Add the bell peppers and dried oregano and fry briefly. Deglaze with broth, bring to the boil and simmer covered for about 25 minutes. In the meantime cut olives into slices.
Puree the soup with a chopping stick. Season to taste with salt, cayenne pepper and vinegar. Arrange soup in bowls or deep plates. Stir a teaspoon of pesto into the soup and sprinkle with olives. Serve garnished with oregano