To make the greek salad, mix the cucumber, tomatoes, and red onion together in a medium sized bowl. Dress with the olive oil, vinegar, salt and pepper, and stir to combine.
To assemble the wraps, spread each pita with about 4 tbsp of hummus. Add a quarter of the greek salad to each pita and sprinkle with the feta cheese. Add the grilled chicken, if using. Wrap each pita with parchment paper or foil and serve.