Grate the onion on a cheese grater, into a bowl.
Add the parsley, ground beef, cumin, coriander, all spice, garlic powder, sumac, salt and pepper. Mix well. Divide into about 1/4 cup pieces. Flatten with your hands until thin circles slightly smaller than the pita.
Cut the pita halfway down the seam and open it up. Set the flattened meat into the pita and spread it out evenly. Press the pita together again.
Heat a skillet over medium-high heat.
Brush olive oil on both sides of the pita and place them on the skillet. Cook for 3-4 minutes on each side, until the meat is cooked through and the pita is toasted.
Mix the yogurt, tahini, and lemon juice in a bowl. Thin as necessary with water. Season with salt and pepper to taste.
When the arayes are done, cut them into quarters. Serve with the sauce.