Damian just sent me this picture of a most remarkable sea slug. It reminded me of a story Rhianon once wrote about a group of post-apocalyptic humans who had mutated to be capable of photosynthesis. Now, that's quite a mutation. Genetic engineering, though, might do the trick.
So here's the plot for a science fiction story, which I give away freely, though if none of you use it, I may use it myself when I have a little more time. A religious cult, more strict about taking life than the Jains, more concerned about non-violent eating than vegans, develop a way to genetically engineer the embryos of their children, and raise a clan of photosynthesizing babies.
You get to take it from there. Are the green-skinned children accepted or persecuted? Do they grow up non-violent, or do they rebel and eat meat anyway? All yours to speculate about.