Heat a large skillet over medium-high heat and cook and stir the ground beef until the meat is crumbly, evenly browned, and no longer pink. Drain and discard any excess grease. Transfer ground beef to a bowl; set aside. Cook and stir the cabbage, onion, carrots, and mushroom in the skillet over medium-high heat until the vegetables are tender, 5 to 7 minutes. Stir in the beef, and season with salt and pepper.
Fill each pita half with the hot cabbage mixture. Top with mozzarella cheese.
