Chop the cucumber, bell pepper, and tomatoes. Thinly slice the onion.
Add 1 teaspoon vinegar to a bowl with cold water. Add sliced onion to the bowl and set aside for 10 minutes. Then drain.
Chop the feta cheese.
In a large bowl combine all the vegetables and the cheese and set aside.
In separate bowl whisk vinegar, olive oil, salt, pepper, and oregano. Pour over the salad and toss to combine. Set aside for 15-30 minutes before serving.
