Yes, you can freeze Quorn once it's been cooked. As long as your meal is cold before freezing, and all the other ingredients are suitable for freezing and reheating, you can keep it in the freezer for up to a month.
When you're ready to enjoy your Quorn product, simply defrost it fully in the fridge and then cook it within 24 hours. Make sure the food is piping hot throughout before serving it.