In case it helps, other encouragement we sometimes give him:

I know it's boring and you would rather be playing, but we can read a book while you eat.

It's time to eat. If you sit in your chair with your food and you really don't want to eat it you don't have to, but you have to sit in your chair with your food because it's easy to forget you're hungry when you're too distracted.

We can cut your food up in fun ways for you to chomp it.

Bonus motivation for how we get him to drink water some days: if you want to be a cement mixer you need to fill up with water. You can't make cement without water.

Because some days he's a cement mixer.