In a small bowl, combine yogurt, cucumber, mint, garlic, and salt. Set aside.
Preheat broiler. Line a very large baking sheet with foil; lightly coat foil with nonstick cooking spray. Place meatballs on the prepared pan. Broil 3 to 4 inches from the heat for 3 to 5 minutes or until heated through, turning once. Slide the foil and meatballs off the pan and onto a wire rack; cover meatballs with foil to keep warm.
Place pita bread halves, cut sides up, on the same baking sheet. Top pita halves with tomatoes, meatballs, and the feta cheese. Broil about 2 minutes or until heated through. Spoon yogurt mixture over pita melts. Top with the roasted red peppers.