Our development pediatrician suggested that you put a small amount on the plate without requiring the child eat it. Continue
doing it till it becomes a familiar food to the child and they'll be more accepting to trying it.

When introducing him to new foods try offering small amounts.

My son is picky too. As much as I tried to do what the other person said it didn't work for my son. My son is 13 year old and still won't try new food. I tried to cut up vegetables to put in with his food and noticed it right away and refused to eat it. Sometimes we can get him to try new food or his older brother can sometimes get him to eat different foods. So when my oldest son is eating something he will offer some to his brother. Good luck

Now a days there are All Sorts of Options and Ingredient alternatives ecspecially because of all of the Special Diets People are on, not to mention their Food Allergies and Sensitivities. Kids on the Spectrum are Alot like most Every other kid.....TheyAall have their Favorite Foods.They can just be Pickier and More Stubborn about What they will eat .Things to keep in mind..... 1rst Kids go by Looks.Ask yourself Does it Look the Same as the Favorite Food Your Child always likes to Eat? If it doesn't You will be Lucky if You can even get your child to Taste it.
2nd Does it Taste the Same?
3rd Don't Forget to take into consideration the TEXTURE of the NEW Foods you are offering.Substitutions have to be the Same or Similar Taste and Texture.
Use as many Healthy Ingredients as possible..........
Homemade Meals are Alot Healthier than Take Out even when you are eating the Same exact foods.
There are All sorts of food substitutions to choose from if necessary.......
Like Cauliflower or other types of Vegetable Pizza Crusts.
And Pizza is something You can make Easily and quickly at home.You can even make it a Family affair.Everyone can help make the Pizza Dough or have the Crust pre made and ready for Everyone to Add their Own Toppings to.If your child will only eat Pizza but won't eat Chicken or Tacos maybe He will Eat Chicken or Taco Pizza? You can even make Mini Pizzas out of Bisquits or English Muffins or with Pita or Nan bread.
There are even Healthy Pizza alternatives thatare offered Pre made in the Frozen Food section. Now You can even get different Healthier options at your Favorite Take Out places.Just keep in mind that
Too many Changes All at once If they are obvious and noticeable will likely be difficult for Your child to accept at least all at once.
There are also Lots of Healthy or at least HealthIER Choices for Chips to Snack on.Beet and Sweet Potatoe Chips are only a few examples.If it can't be More Nutritious and Less Fats at least let the Foods your child eats be More Nutritious.Your child may even Need the Extra Fats and Calories if they are Really Picky about What and How Much they Eat.
You can also make Your own Chips.
My kids love homemade Kale Chips. They are Super Crispy and So Quick and Easy to make......
No Hot Grease or Frying. Necessary....
You just season as you desire and then Toast them on a Cookie Sheet in the Oven.
If you go on line and Google Healthy Recipes for Kids or Picky Eaters You will find More Recipes than You can possibly begin to choose from......and it would be a Great Experience for All of Your Family to Try NEW Foods and HEALTHIER Recipes.If You don't know already Kids on the Spectrum are Greatly affected by what they Eat.Junk Food and Excess Sugar, Dyes and Additives can Not only affect overall Health but just as Important they adversely affect Mood, Temperment, and Behavior.
Don't be afraid to Try NEW things.