Heat the oven to 350 degrees F. Place the pita breads on a baking sheet and bake until they are dry, about 15 minutes. Remove from the oven. When cool enough to handle, break the bread into large bite-sized pieces.
In a small bowl, whisk together the dressing and sumac, if using, and add salt and pepper to taste.
In a large salad bowl, combine the tomatoes, cucumber, red onion, green onion, parsley, and mint, then add the pita pieces, the purslane if using, and the romaine, and toss with the remaining dressing. Serve immediately.