I have an almost 7 year old who is rarely "hungry" to the point that he loses weight at times. I know that there is already a natural consequence to not eating, but your son needs to learn that he feels better (and will be healthier) if he eats regularly.
We put up a sticker chart. At first, our son got to go to the dollar store (He is addicted to the dollar store!) when he got a small number of stickers on the chart, with stickers as the reward for eating at mealtime. The number of stickers has gradually gotten bigger, and eventually we got rid of the chart altogether as it was no longer necessary. The point is that sometimes kids need some external motivation, along with positive praise, to develop good habits. Hopefully, this will help you to end the power struggle. (I know it worked for us!)
P.S. We also put up a sticker chart for our younger son, which really helped motivate our almost 7 year old to get his stickers so he could go with his brother!