Cut potato in large chunks. Place in a small saucepan, cover with water and bring to a boil. Reduce heat and simmer until just tender. Drain, return to pan and sprinkle with vinegar. Cool.
Cut tomato, cucumber and green pepper in large chunks. Combine in a large bowl with potato and onion slices. Add olive oil. Toss gently. Add lemon juice, salt and pepper to taste. Toss again.
Pile the salad on a platter. Sprinkle olives and dill over it. Cut feta in large slices and lay on top.