Lightly toast the pitas, if you prefer, either on the lowest setting in your toaster oven or at 400F for 2-3 minutes. You can skip this step if you do not want to toast the pitas.
Layer all the ingredients onto the pitas: Spread ~2-3 tablespoons Greek yogurt onto each pita. Top each pita with ~5 cucumber slices. Season with salt & pepper, if desired. Add a 1/4 cup smashed chickpeas, 1-1.5 oz feta cheese to each pita. Sprinkle with 1 teaspoon za'atar and fresh parsley leaves. Serve immediately: eat the pitas whole or slice into quarters.
Some other topping ideas: pickled onions, shredded chicken, pickles, canned tuna, drizzle of sriracha.