If you chop the chicken up really small, it will mix in better with the rice (the rice needs to be really well cooked and soft - I've found basmati works better than long grain, as it's more inclined to go soft and a bit sticky).
It's ok to use a little pasta, or even some plain toast, but the thing is that both contain wheat, which is a common allergen, and thus not necessarily as easy on the tummy as rice.
Having said that, my Alfie wouldn't eat rice either at that age when his tum was upset, and found a way of leaving most or all of it. So I did his chicken with some little bits of dry wholemeal toast, and he was fine with it. A couple of times I gave him a little scrambled egg with toast, instead of the chicken with rice/toast, and that went down a treat as well.