Add the tomatoes, cucumbers and onions to a large salad or serving bowl.
Drizzle with the olive oil then toss with oregano, lemon juice and capers (optional), until combined.
Season with salt and pepper then let sit for 10 to 15 minutes for the flavors to marinate.
Top with the pieces of feta and serve.
Notes
Soak the sliced red onion in cold water for a few minutes before adding it to the salad. This softens the sharp bite while keeping the onion crisp and flavorful.