C.S.
Slowly sneak it in his food. Start with a spinach leaf, chop it real small like parsley flakes and add it to his spaghetti or soup.
Increase it little by little. This will change his pallet to like it. My 7 YO will now eat green beans, spinach, carrots, corn, broccoli, cauliflower, chopped cooked onion, tomatoes, etc. She is pretty good about eating now.