For really picky eaters, the best way is to sneak in relatively neutral-tasting vegetables into the food they normally love. For example, pureed courgettes with pasta or rice. My experience is also that you need to be persistent and offer them vegetables regularly even if they refuse to eat them. As long as you put some vegetables on their plate, chances are at some point they will start eating. Especially if they see you eating the same. I have never seen a kid that absolutely refused all vegetables all the time unless parents themselves did not eat or care or gave up offering.

But if he eats fruit, then there is no reason for concern. Apparently, everything you find in vegetables can be found in fruit as well.