I bought the above and the package says 'oven cook from frozen, if allowed to defrost reduce cooking time accordingly'.
If allowed to defrost safely, can I shallow fry it in a wok, or HAS it got to be oven cooked?
You can cook it however you like, it's meat. I would suggest slicing it up and stir frying it if you are using a wok. If you want to keep it whole, use a frying pan with a thicker base and place a heavyish lid on top of the breast with a piece of baking paper between the two to even out the thickness of the piece of meat. That will help it to cook more evenly.
Cooking chicken from frozen isn't a great idea because you'll have to overcook the outside in order to cook the inside. If you were to cook from frozen oven cooking is one safe possibility, which is why the instructions say to do that - it's for the avoidance of lawsuits. Thawed you can cook it any way you like, there's no limitation on method just because it was once frozen.