Let him go shopping with you and help prepare the food, this makes them want to try it more.
Honestly, it sounds mean, but if want him to try something, leave it as the only option. Put something in front of him for lunch, if he wont touch it cover it and put it back into the refridgerator, let him go, but with NO SNACKS until dinner time, where you take it out and put it in front of hin again, if he wont eat it, dont give him anything else. Chances are he will break down and eventually try the food. You wont be starving him. He needs to learn to try new foods because the diet you say he is on now is not healthy and is also forming the habits he will have for life. I would drastically change the way you feed your sons, to get this one out of this habit, and to make sure you are not in this position two years from now with your two year old. I have done thsi with my daughter before, she knows she needs to at least try any food i put in front of her, and she does now, but it took training. If she really doesn't like something I obviously dont make her eat it, but most of the time she finds that she likes it.
Does your son like dips? My daughter loves meals which she can dip stuff, like taco dip is about the only dish she will eat that has ground beef in it(she does not care for meats). By the time I add teh beans and veggies to it, the meal is healthy an dfun for her because it comes with tortilla chips.
Also, fruits and veggies to dip are fun. Try apples and peanut butter, that's my daughter's favorite.
Does he eat mac n cheese, there are a million ways to add veggies to mac n cheese that kids will eat. I have a recipe that includes a salsa and a ton of corn that my daughter loves and provides much more for her than a simple box of Kraft.(and tastes so much better)
It's all in the recipes, and mashed pear, I may have been upset for someone to put that on my lip as well, he is not a baby, lol.
I have some very kid friendly recipes, (most are meatless as my daughter does not care much for meats besidies fish sticks or chicken tenders), but if you are interested in some please message me, and good luck getting your son to start eating better. Kids can be stubborn and it is hard to get them on teh type of diet you want.