RE: "How can we get him to change his eating habits?"

"My grandson has ASD. He is age 7. His diet consists of cheese, eggs, bread, milk, juice, wieners, fish, hamburgers, chicken, mashed or French fried potatoes and, on occasion, chocolate and bananas. He will eat no pasta, vegetables, or any other fruit. Does this eating problem go along with Autism? How can we get him to change his eating habits?" 

Your grandson’s disorder may cause unusual reactions to new foods and he may not want to eat them. To him, they may taste bitter, salty, or just plain awful. They may smell bad (to him). He may dislike the textures of new foods. Consequently, he doesn’t want to eat foods that cause these reactions.

Compared to some other kids on the spectrum, your grandson’s diet is not that terrible. He gets protein from eggs, milk, cheese, wieners, fish, hamburger, and chicken  ...grains, which provide B vitamins, from bread and hamburger and hot dog buns  ...some vitamins and minerals, including vitamin C, from juice, potatoes, chocolate, and bananas  ...and calcium and vitamin D from milk and cheese.
 
==> Parenting Children and Teens with High-Functioning Autism: Parents' Comprehensive Handbook

All in all, his diet could be worse and is not much different from what many neurotypical children eat. However, his diet would be more nutritious if he ate more fruits, vegetables, and grains. Perhaps he would try some whole grain cereals. 
 
Many autistic children like Life cereal or Cheerios. See if he likes popcorn, which is a whole grain (don’t load it up with a lot of butter, though). Try whole grain breads, hamburger and hot dog buns. 
 
He might like whole grain rice. Try it mixed in a cheese and chicken casserole. Most kids like macaroni and cheese. See if he does. Try tacos made with whole grain tortillas, hamburger, and cheese. You might be able to sneak in some chopped tomato and onion. Use low fat hamburger and 1% milk.

See if he will drink different types of fruit juices. There are new ones on the market that are delicious and have a serving of fruit and one of vegetables in each glass. Many fruits may taste sour to him. If he likes cereal, slice half of a banana on it. 
 
 
Canned peaches and pears are sweet and may appeal to him. Cut up fruits into bite sized pieces so they are easy to eat. Don’t chastise him if he doesn’t eat them; maybe in the future he will. Make small apple or blueberry muffins. He might like them, too. Yogurt with fruit is an option you could try.

As far as vegetables are concerned, it may be an uphill road! But, sometimes vegetables can be hidden in other foods, for example, in those juices mentioned above. How about putting some onion in his hamburger? Potatoes are vegetables and he likes them! Try oven frying the French fries instead of frying in oil. Blend some cooked cauliflower into his mashed potatoes. 
 
He may not notice the difference. He may like sweet potatoes. He might like creamed corn or cornbread. Does he eat any soup, such as pea soup or vegetable? You could try tomato soup made with milk -- he might like it. If you put finely chopped, frozen carrots and peas in a chicken/cheese casserole, he might eat them. Avocado has a bland taste, and you could mix it into his hamburger patties.

It’s very important not to make “a big deal” about what he doesn’t eat. If you do, eating will become a power struggle. Offer various new foods along with ones he likes. If he doesn’t like them, don’t make an issue of it. Some battles aren’t worth constant fighting, especially when his diet isn’t too bad to begin with. Keep serving some new foods along with the old ones. Avoid serving soda pop and sweets so he doesn’t fixate on them.

Lastly, make sure he has a multivitamin each day. Get one that is chewable, tastes good, and has a cute shape. Also, drinking Ensure or Pediasure is a good way to supplement his diet with vitamins and minerals.
 
Best of luck!