If you have a juicer, you can make some wonderfully nutritious fresh fruit and vegetable juices that will be packed with vitamins and minerals. Unfortunately juice is low in fiber, so he will have to get that from other sources, like whole grains and legumes. Fruits and vegetables are often accepted in one form but not another. If your son is refusing to eat cooked carrots, perhaps he would prefer them raw, in sticks, that he can dip into his favorite dip. If cooked peas are not accepted, perhaps he would like them fresh, and he can take them out of the pod.
Most grocery stores carry fresh peas year round.
Many other vegetables can be finely grated and added to spaghetti sauce and will never be noticed. Try it with carrots, summer squash, green peppers and onions. Mixing finely chopped spinach into the ricotta cheese mixture of stuffed shells is a way to 'disguise' the vegetable. Low-fat pumpkin bread is a good way to serve pumpkin. Pureed baby food vegetables or fruits can be added to muffins.