I offer Butter a salad a couple days a week. His main feeder is silkworms, so I put a couple pieces of dark greens in his bowl, shred some carrots, and add what ever fruit is around (just a shred or two of something). I stick the silkworms on top of it, and he picks off the silkies, and then if he is interested, he will eat the salad.
I'd say he eats the salad maybe once a week. Just depends on his mood. If I notice that he's eating the plants in the enclousure, I'll give him more greens and vegies.