I think the issue is that unseasoned plain vegetables (particular broccoli, spinach etc) are just not particularly tasty on their own. Adults usually prefer them seasoned (whether with salt, stir-fried with soy and chilli, with garlic butter, lemon juice, vinaigrette, cheese, etc). And we know that they're good for us and we should be eating them - so imagine how much less motivation a toddler, with no real sense of delayed gratification, has. Chips and chicken nuggets, on the other hand, set off all kinds of pleasure receptors in our brains. Salt ! Fat! Potato! All delicious.
So if you serve plain vegetables as a side dish to nuggets, he is more likely to eat the latter and the veg will seem even plainer by comparison.
I don't think you should always hide vegetables but you might get him to eat more of them if they are intrinsic to a tasty dish rather than a plain side dish. So, for example, I make this stew cooking.nytimes.com/recipes/1019772-spiced-chickpea-stew-with-coconut-and-turmeric (minus the salt and easy on the chilli) for my daughter and now she loves the kale in it (she already loved chickpeas). Or I make chicken stew with onions, peppers, carrots and tinned tomatoes (plus lots of garlic and smoked paprika) or Thai curry with baby sweetcorn and peppers, or risotto with prawns, leeks and peas. Or you could add mushrooms and kale if you make macaroni cheese, for example. I add finely chopped kale and fennel to my fish pie (as well as peas).
I'm sure purists would say that it's better to get kids to enjoy plain vegetables, but I would honestly rather that she eats them in a healthy format without me having to hide them.
Another idea is to get him to help a bit with cooking, e. g. washing the vegetables.
Hope that helps.