I have a young bearded dragon, and he would only eat crickets and not even bother looking at the greens.

We're still in the taming process so when I went to pick him up yesterday and he opened his mouth to show me how bad he was I just stuffed a little piece of mustard greens in there. I did this every time he showed his teeth (around 5 times) until it was time to put him up.

When I offered him his salad this morning I just tried to offer him a small leaf by hand before running out the door, and he took it like it was candy. Ended up hand feeding him several pieces before he refused.