Chop the onion and garlic and fry in oil until translucent. Add the coarsely chopped tomatoes and simmer on low heat for 20 minutes. Add the clear soup, season with chili and salt and simmer for 15 minutes.
Break the tortilla chips into bite-sized pieces. Remove the skin from the avocado and cut into 1 cm cubes. Cut the feta cheese into 1 cm cubes.
Arrange the soup in plates and evenly distribute the avocado, feta cheese and tortilla chips on top. Garnish with a tsp. of sour cream and season individually with a lime quarter.