Pasta dishes with a sauce and meat they like that have some texture can be a godsend. Just chop the vegetables very fine and make sure they have a good steam in the sauce so they pick up most of the flavor. Mostly, they don't even notice.
Sometimes you can mix in cauliflower with mashed potatoes.
If you fry things, you can mix some chopped green beans or the like into the breading if the flavors are strong enough to offset.
And if all else fails, carrot cake without telling them it has carrots.