Hi Blondie,
you are correct about frozen chicken breast being used by the restaurants, a Bengali friend used to own the Fareham Tandoori near Portsmouth and i have been in the kitchens and seen the frozen blocks of chicken breast myself.
He told me this was the most cost affective way of buying chicken with no actual waste, he also told me that other restaurants were buying from the same supplier.
I was also told that in that in the very early days of Indian restaurants they used boiler chicken which is basically a very old hen and of course although very cheap to buy the meat was very tough so the whole chickens along with all the ingredients were cooked for hours to tendarise the meat, the onions were not chopped they were left whole and gradually fell apart with the long cooking process.
After hours of boiling the chef then had the task of blending the onions and in those days it was done with a hand blender, the meat was then just picked off the carcuss ready for use.
Jon.