Make the sauce. Set aside 1/2 cup of the yogurt. Add the remaining 1/4 cup yogurt, the mint, lemon juice, and salt to a jug and blend with a stick blender until green and runny. Stir in the reserved yogurt to thicken it, then refrigerate. Mix the meatballs. Place the lamb, onion with its juices, panko, egg, garlic, cilantro, cumin, coriander, paprika, cinnamon, cayenne, salt, and pepper in a bowl. Mix well with your hands.
Shape. Scoop 1 heaping tablespoon at a time and roll into balls, making 20 to 24 meatballs.
Cook in batches. Heat the oil in a large non stick skillet over medium heat. Cook half of the meatballs for 7 to 8 minutes, turning to brown all over, until cooked through to 160 degrees F. Move to a plate and repeat with the remaining meatballs.
Oven option. To skip the stove, bake the meatballs on a lined sheet pan at 400 degrees F for about 15 minutes until they reach 160 degrees F.
Prepare the pita. Cut the pita breads in half, warm for 10 seconds in the microwave, and gently open each pocket.
Assemble. Stuff each pocket with lettuce, tomato, red onion, and 2 meatballs. Drizzle with mint yogurt sauce and top with extra cilantro.