My son, is like that too.
I find that he is a "grazer." He does not eat a ton, per sitting, each time, like his sister who has a hearty appetite.
My son, eats until he is full. Then that is it. And each day it can vary. Like an adult.
I find, he will eat "better" if we sit out on the patio. Or, if I put things on a 'small' dinner plate, instead of a regular adult sized plate. My son gets put off by "seeing" tons of food on a big plate, it overwhelms him, and he'll immediately say he can't eat it all. Which I dont' expect him to.
Then, he likes homemade soups... and i mince everything up in it real small, cook it down real well, and I give him a straw to "eat" it with. So its funner. He likes that and he will eat it all up.
Then he likes sauces... with anything. So that's fine.
Next, remember that a "serving size" for a Toddler is in terms of TABLESPOONS or teaspoons. Not a serving/portion size like we adults are used to eye-balling.
If I serve my son, in these amounts, then he's more prone to eating it. But my son, is again, not a "big" eater.... like his sister. I have just learned what his eating "style" is.
Or my son will eat if something is on skewers. But I make the chunks small, his size.
Or, try getting that Jerry Seifeld's wife's book. Its about pureeing things/veggies into foods, and even cupcakes. Its real good and tastes good.
Mostly though, a child goes through eating phases and taste changes. So, for me, I don't push it. Sure, introduce things, new things... but don't bring attention to it. Just put it there, on the table. Let him explore it.
My son, again, will try something often times, if there is some kind of sauce with it, or salad dressing to "dip" into. He likes to dip things. So that's fine.
And too, I find it can be all about the size of the food pieces... my son won't eat something if its too "big"... so I cut it up smaller, even though he can chew and break the pieces apart.
Not all kids eat BIG or lots, per sitting. Just like adults... some eat like a bird, some eat HUGE and fast, some eat slow and little. Then, the main thing is, that they know when they are "full" so that they don't eat for emotional reasons. If my kids genuinely say they are "full" even though there are things left on their plate, no biggie. They know their tummies.
Tastes and eating will ebb and flow.
Just some ideas,
all the best,
Susan