1) Wash and dice the tomatoes and cut the cucumber into small rounds.
2) Slice the green pepper and then thinly slice the onion.
3) Put the tomatoes, cucumber, green pepper and onion in a large bowl.
4) Add the olives and salt and pepper. Toss well to mix.
5) Add the olive oil, mix and top with the piece of feta cheese.
6) Sprinkle oregano all over.