Season the cucumbers and tomatoes with salt and pepper.
Dry all of the vegetables with paper towels. Combine the cucumbers, tomatoes, red onions, bell peppers, olives and feta cheese in a large bowl. Drizzle with dressing and season to taste with salt and pepper. Add romaine or baby spring mix, if using. Top with banana peppers.
To make the dressing, whisk together the olive oil, red wine vinegar, garlic, oregano and Dijon mustard. Season to taste with salt and pepper.
*2 cups of romaine lettuce or baby spring mix can be added.