Having been thoroughly indoctrinated about thoroughly defrosting poultry before cooking, I now find 1.5 Kg frozen turkey breast joints with the cook from frozen instruction. How can this work? Surely by the time the centre is defrosted and cooked the rest will be dried out.
I guess you are talking about a pre-seasoned convenience product in an oven bag like this Butterball Ready to Roast boneless skinless turkey breast?
Well, the website writes:
Boneless Turkey Breast. Contains up to 25% of a solution of Water, contains 2% or less of Salt, Sugar, and Sodium Phosphate to enhance tenderness and juiciness.
This is like a super-brined piece of meat that consists of 3/4 meat and 1/4 watery brine. You don't want to thaw that because during thawing you'd likely lose a lot if the additional liquid. In the oven, the product thaws and the additional water keeps the meat moist, the sealed bag contributes to this.
It's imho not a classic roast (different ingredients, different preparation method), for an untreated turkey breast the "defrost first" rule is still valid.