Heat the stock in a large frypan over medium-high heat. Season chicken with salt and pepper and place in the frypan. Cook 15 minutes until chicken is almost done.
Place asparagus, red capsicums and garlic in frypan. Continue cooking 10 minutes or until chicken juices run clear and asparagus is tender. Place tomatoes in frypan during last 2 minutes of cook time. Sprinkle with vinegar. Top with mozzarella cheese to serve.