There are lots of veggies that you can add to dishes that you can hardly tell are there. If he is really new to veggies he can always start with frozen and canned and work his way to fresh. Peas and spinach and extra tomatoes are easy to add to pasta sauces. Chili is another great recipe to hide veggies in. It's nice and meaty and spicy, throw some onions, peppers, and corn in there. Someone else recommended pizza--another great idea, zucchini/squash are easy to add to pizza and have a mild flavor.
Check out some recipe sites: allrecipes.com or cookinglight.com (you may have to register for this one)