Combine the red wine vinegar and red onion in a large bowl and let sit while you prepare the other ingredients. (This will take away some of the bite of the onion).
Add the cucumber, tomatoes, mint, olives, and feta to the bowl and drizzle with the olive oil, tossing gently to combine. Season with salt and pepper to taste.
Serve immediately with crusty bread to soak up the extra vinaigrette.
*I like using a combination of red and yellow grape tomatoes if they’re available.