Wash and cut cucumber into slices. Sweet peppers are washed, cored and cut into slices. Wash tomatoes and cut into slices. Clean the bulbs, cut into thin rings. Cut feta cheese into cubes and mix with oregano. Drain olives from the brine, add the cucumber, bell pepper, onion, tomato and feta. Mix olive oil, lemon juice, salt and pepper and pour salad dressing. Stir.