With kids who are fussy eaters, I would just continue to give what he likes, but with each meal serve a healthy vegetables side dish that he must take one bite of. Just one bite, and tell him he doesn't have to eat any more than that. Don't make a big deal out of it, but when takes the bite tell him you're happy that he at least tried something different. If he wants more that's great, if he doesn't, that's great too, good job trying something new. The idea isn't to get him to eat a portion of it, but to taste it, and if he feels that you don't care either way he will be more willing.
You can make it interesting, au gratin, or with special dressings etc. and variety. The idea is to get him to at least try different things and also they say that once a person has eaten something 10 times then they'll be used to the new taste and may even like it.
This post reminds me of how naive we parents are. Talk about lambs to the slaughter.
I think we should not be allowed outside of the home unless accompanied by a child.

I recall hearing my ex-wife saying the same thing.
"Just try a little of the vegetables. Take one taste and if you don't like it you don't have to eat it".
Then my sons take one taste and wrinkle their noses.
Then she complains to me they won't eat their vegetables.
Then I ask my sons why they aren't eating their vegetables.
My sons say, "its okay dad, mum said we don't have to eat them".
You must shift the focus from the vegetables.
Cut long stalks of carrots, celery etc and provide tasty dips.
With meats, serve in small slices or chunks with a central dish of lettuce as the Koreans do. Eat the meats like a fajita replacing the flour with lettuce, which since their is only a centrally located supply, they will fight over.
Kids love to eat with their fingers; they know how much parents disapprove and it purges them of inherent mischief and stubbornness.
