Preheat the oven to 400 degrees F. Peel the pitas apart and brush with oil and sprinkle with with salt and sumac on both sides. Cut the bread into bite size pieces (about 1 inch x 2 inch). Lay the pita in a single layer on a wire rack over a baking sheet and bake until crisp, about 8-12 minutes. Allow to cool.
In a bowl combine and whisk together the dressing ingredients: olive oil, lemon juice, sumac, garlic, black pepper, and kosher salt then set aside.
In a large bowl toss the lettuce, grape tomatoes, cucumbers, red onion, pepper, parsley, mint, half the pita crouton, and half the dressing together with tongs until well coated.
Place the dressed salad in a serving bowl and sprinkle with sumac. Serve with the remaining crouton and dressing on the side.