Your hungry so quick because of the type of food you ate.
Bagels are full of white flour, white flour converts to sugar VERY quickly, so your body floods with sugar, gets its quick energy fix, and then falls just as fast, hence making you hungry again
On the other hand, if you ate something like an egg with veggies & flax seeds or any other type of nuts, that fat, protein, and fiber would take longer to digest and keep you more satisfied.
For those of you that say you are eating oatmeal and then getting hungry, its not about the oatmeal, its about the amount your eating of it, you should probably have a bigger serving to make you feel full or satisfied.
All in all, if your body is hungry, feed it with good wholesome food and you should be just fine