Drain tuna and corn well. Cut half of the bread into cubes. Heat 4 tablespoons of oil in a frying pan and fry the bread cubes all around until golden brown. Clean and wash the tomatoes and cut out the stalk.
Cut the tomatoes into slices. Peel and roughly dice the onion. Wash herbs and dab dry. Chop parsley roughly, cut chives into small rolls. Coarsely crumble feta cheese. Mix the remaining oil and vinegar, season with salt and pepper.
Mix tomatoes, corn, tuna, onion, herbs and vinaigrette. Sprinkle bread cubes and feta cheese over it. Arrange the salad in a large bowl, add the rest of the bread.