I would suggest breaking your breakfast in half - eat a snack, such as a granola bar or a banana/piece of fruit, before working out. It will give you more energy and keep you from binging later on. Then eat something small again after you work out, like something with protein that will reinforce your exercise. I have the same issue, except I don't exercise in the morning.....I have to hold myself back from overeating by accident so I don't feel too full. Usually I have fruit and a piece of toast, or a small bowl of cereal topped with berries/a banana.
I would think you'd be less likely to overeat as well if you remind yourself that you don't want to spoil all the hard work you just did at the gym!