The word comes from Australian slang, but may have originated in the U.K.
like calling someone a spoon
or it could be a good thing.
Therefore if someone should say you are a 'good onion' its alll gooood :D
Gurinda: Lol, you onion
Aaron: Hey, ive made some friends that are nice to me
Kat: Tell you're friends i like them Aaron, they are Good Onions :)