I'd just continue to serve balanced meals and he can eat or not eat. It's our job as parents to provide healthy food at regular times - it's his job manage what and how much of it he eats. I wouldn't start serving up endless pasta and/or pbj!
This ^^^
In terms of hungry, honestly we in the western world have quite a "big" idea on what what is a normal amount of food... I saw recently when visiting a friend who'd had a baby that the size of a "normal" stomach should be the size of a person's fist, so total food for the day really should be about 3 fists worth
Also it is really worth looking at milk consumption... I came across this yesterday when I was reading up on the nutritional needs for my boys.
"Just small amounts of energy-dense milk can fill a little tummy quickly. Feeling sated, your little one might turn away from other foods and meals, thereby causing them to become deficient in other nutrients. For example, toddlers and young children require between 1200 and 1500 calories a day. If a two-year-old drinks just 300ml of milk, they’ve consumed 20% of all their calories for that day – from just one food source.
Too much calcium – which can add up quickly in a child’s case – can interfere with iron absorption, which in turn has been linked to fussy eating.
Incidentally, the above explanations might shed new light on your fussy eater: perhaps your child has been overfilling on cows’ milk and/or is low in iron from too much calcium?