My  10 week old BC puppy had diarrhoea and the vet advised us to feed him on chicken and rice for 3 days.  How much chicken and rice should I be feeding him per day?  (I've bought chicken breasts) I've been giving him a small bowlfull 3 times a day with a teaspoon of probiotic yoghurt and he still seems hungry!

That seems fine. However if he still had bad diohrea after three days I would be taken them back to the vet

That seems fine. You could feed a little bit more as I was feed four meals a day at this age.  However if he still had bad diarrhoea after three days I would be taken them back to the vet. There should have been an improvement in the first 24-48 hours.