Cut lamb into 1/8-inch-wide strips; place in a small bowl. Sprinkle garlic powder, rosemary, and salt over lamb; toss to coat.
Coat a small nonstick skillet with cooking spray; place over medium-high heat until hot. Add lamb strips, and cook 5 minutes or until lamb is browned on both sides. Drain and pat dry with paper towels.
Combine cucumber, tomato, and yogurt, stirring well. Spoon lamb evenly into pita halves, and top evenly with cucumber mixture.