My sister and I used to watch this movie when we were little (1980's) that had a green dragon who ate these things that looked like white onions. I remember a very specific scene where he is in a cave eating the 'onions.'... any ideas? It's driving me crazy!

Possibly "The Flight of Dragons"

The Flight of Dragons (1982) (http://amazon.imdb.com/title/tt0083951/)

Pete's dragon?

No it wasn't flight of the dragon or pete's dragon or puff the magic dragon... those were all good though.

I'm afraid this may have a been one of those rare pbs special kind of movies. I think the dragon may have been some sort of an outcast in the movie... maybe? Thanks for your suggestions!