What is the best grain free, sensitive system low fat dog food?

Im looking to change my dogs current food. He has a health issue and needs to have low fat food. He also has a sensitive GI system. 2 months ago he had a infection in his colon and needed to eat chicken and rice. He is all clear from the infection and is back to normal. I started to introduce his kibble slowly back into his diet. I started to add 5 kibbles. The day after I started to re introduce the kibble he began to have GI issues again. So, I believe he may have a allergy to grain or the previous food. I worry that the chicken and rice does not have all of the nutrients he needs in his diet. The food he previously ate is California natural organic low fat lamb and rice. Any suggestions?