Place the sliced cucumbers, chopped garden tomatoes, onion, and green olives in a large mixing bowl. Toss gently to combine.
Whisk the mayonnaise, Parmesan, balsamic vinaigrette, onion powder, garlic powder, Italian seasoning, and red pepper flakes in a separate bowl until smooth.
Pour the dressing over the vegetables and fold gently until everything is evenly coated.
Transfer to a serving bowl and top with the halved cherry tomatoes. Garnish with fresh basil if desired.
Cover and refrigerate for about 30 minutes before serving. Stir gently once more and serve chilled.