1 With the rack in the middle position, preheat the oven to 425°F (220°C). Line a baking sheet with a silicone mat or parchment paper.   2 In a skillet over medium-high heat, brown the meat in the oil, breaking it up with a wooden spoon as it cooks. Add the onion, garlic and spices. Continue cooking for 3 minutes. Season with salt and pepper. Remove from the heat.   3 Transfer the mixture to a food processor. Add the tomato, yogurt and herbs. Pulse the mixture until just creamy. Adjust the seasoning.   4 Place the pitas on the prepared sheet and spread each one with one-quarter of the meat mixture. Bake for 12 minutes or until the flatbread is light golden brown. Let cool, then garnish with parsley and mint, if desired.