Wash tomatoes, peppers and cucumber. Eighth or slice the tomatoes. Halve the bell pepper, remove the seeds and white skins and cut into thin strips. Finely slice the cucumber with the skin. Cut the peeled onion into thin rings. Crumble the feta cheese. Wash and pick the lettuce.
Arrange all the ingredients in a large bowl, with the drained olives on top. Dress with a sauce made from vinegar, salt, pepper and olive oil.