Optional: Carefully separate naan bread into 2 pieces and then cut into 1-inch pieces. Spread in single layer on the baking pan of a toaster oven. Drizzle with olive oil and bake in the toaster oven (350 degree F) for 10 minutes or until brown and crispy.
Slice the cucumber, green pepper and tomatoes into cubes of desired size (I sliced them into 1-inch cubes).
Place the sliced vegetables in a large bowl. Add the green onions, cilantro, parsley and the finely chopped mint.
In another large bowl, whisk together the olive oil, lemon juice and sumac. Season with salt and pepper to taste. Add the chicken and vegetable mixture and toss to combine.
Before serving, add the crispy naan bread cubes to the salad, if using.