I kinda do what the previous mom says, but I only ever offer my kiddos healthy stuff, so I don't worry too much about them boycotting a food group - it's typically pretty short-lived.
One thing I've heard a friend mention is pureed cauliflower in scrambled eggs and mac-n-cheese.
Something I did for my daughter when she was around 2y old was use an ice cube tray. I put small carrot sticks, trees (broccoli), clouds (cauliflower), nuts (almonds/ walnuts), and fruits in all but 2 of the ice cube holes. In the remaining two I put "dip" - for us that was yogurt and homemade dressing (ranch, onion vinegarette). This was her snack tray in the fridge for a while. If she was hungry between meals, this is where I directed her. Also at meals, I would let her have dip as well (ketchup being added to the list of options).
Also, if he likes fruit, you could make fruit smoothies. I use my blender. This is a great place to add veggies! I usually use some stronger flavored fruits like banana, kiwi, and berries. Then I'll add cooked/steamed pureed veggies like cauliflower, broccoli, edamame, whatever else that is on hand that isn't too strong tasting. I'll also add greens (spinach, kale, red chard) in small amounts. Catherine thinks it's fun to have a spotted shake :-) I don't put enough greens in to be tasted, so for her it's all how it looks :-) I also use yogurt and a few ice cubes in my smoothies. If you'd like some specific recipes for smoothies, feel free to emall me
HTH
K. H, mama to
Catherine, 4y
Samuel, 15m