Food!

Ah, food. We all eat it. Morgan eats it. I've considered myself lucky that Morgan isn't a very picky eater and more often than not finishes everything on his plate. Now I'm beginning to worry though. Am I feeding him too much? How much is too much? If I continue at this rate will Morgan get unhealthily over weight?
For breakfast Morgan usually has a bowl of cereal. His bowl is filled nearly as much as mine and he eats every morsel. For lunch he might have chicken nuggets. He eats six of them because that is how many I give him. If I gave him seven he would probably eat them all. Morgan can and does eat a whole can of Spaghettios all by himself! For dinner I'll fill his plate with whatever we're having, (barring broccoli, he won't eat that) and he polishes it off most of the time. A whole baked potato, a HUGE serving of spaghetti, (I think it's probably his favorite food). He even eats healthy servings of green salad.
So, all of you experienced parents out there, should I cut down on the serving sizes? Morgan isn't fat, he doesn't have the fat rolls or anything, but he isn't a little skinny twig. He's very sturdy. So what should I do?