Cut the tomatoes into quarters according to size, then cut each slice in half diagonally. Remove the peel from the cucumber and cut it into 1 cm slices, then cut them in half again. Remove the stalk and seeds from the peppers and cut them into thin strips. Remove the skin from the onion and cut it into fine slices.
Arrange tomatoes, cucumbers and onion slices in portions on plates, sprinkle with salt and pepper. Add olives and feta cheese cut into small cubes and sprinkled with oregano. Finally, drizzle with vinegar and oil to taste.