Where I live loose meat sandwiches are know as made rights, this is a Mediterranean take on this favorite. You can use tzatziki sauce (cucumber/yogurt sauce used on Gyros) in place of the feta sauce to give it a more gyro kind of touch.
Heat the olive oil in a large skillet over medium-high heat. Stir in the lamb, and cook until it begins to crumble. Add the onions, and continue cooking until the lamb has browned and the onions have softened, about 5 minutes more. Drain off any excess fat, then reduce the heat to medium-low, and stir in 1 teaspoon lemon zest, 1/2 teaspoon dried oregano, 1/2 teaspoon garlic powder, 1/2 teaspoon salt, and 1/2 teaspoon black pepper. Stir 1/4 cup lemon juice into the water, then pour 1/4 cup of this mixture into the lamb. Cook until the liquid has mostly evaporated, then stir in another 1/4 cup, and cook again until mostly evaporated. Continue adding the liquid 1/4 cup at a time until you have used all of it. This should take about 30 minutes in all. The meat should look moist, but not be sitting in liquid.
While the meat is cooking, make the feta sauce by placing the yogurt, feta cheese, 1 tablespoon lemon juice, 1/4 teaspoon dried oregano, 1/4 teaspoon garlic powder, and 1/4 teaspoon lemon zest into a blender. Puree until smooth, then season to taste with salt and pepper. Set aside.
Spoon the lamb mixture onto warmed pita bread. Top with the feta sauce to serve.
Per Serving: 390 calories; protein 21.2g; carbohydrates 33.1g; fat 18.8g; cholesterol 64.9mg; sodium 684mg.