Method:
Preheat the oven to 425°F. Spray oil a small baking sheet.
Cut the top third off pitas. Tear 2 of the tops into pieces with your fingers and place the pieces in a small bowl; save the remaining 2 pita tops for another use. Add milk to the bowl and let bread soak until very soft, about 15 minutes.Combine beef, onion, oregano, allspice, pepper and 1/2 teaspoon of the salt in a medium bowl. With your hands, gently squeeze excess milk from pita tops; add bread to bowl with meat; discard milk. Mix with your hands or a rubber spatula until well combined. Form the mixture into 16 balls, each about the size of a ping-pong ball. Place on baking sheet and bake, shaking the pan once or twice, until browned and cooked through, 10 to 12 minutes.
Meanwhile, combine yogurt, cucumber and lemon juice in a small bowl. Fill each pita with tomato, lettuce and 4 meatballs. Spoon yogurt sauce on top to taste.