How to Make It
Stir yogurt, lemon juice, 1 tablespoon mint, and ¼ teaspoon salt in a small bowl; set aside.
Cut onion in half lengthwise. Finely chop 1 onion half and thinly slice remaining onion half; set aside.
Heat a large grill pan over medium-high. Mix lamb, finely chopped onion, garlic, cumin, and remaining 2 tablespoons mint and 1 teaspoon salt in a large bowl until well combined. Form into 20 small, oblong meatballs. Coat grill pan with cooking spray. Cook meatballs until browned and a thermometer inserted in thickest portion registers 160°F, turning once halfway through, 7 to 8 minutes.
Spread yogurt mixture on warm pitas. Top with meatballs, thinly sliced onion, cucumber, tomato, and cheese. Drizzle with oil.