Enjoy watching an Oscar doing what Oscars do...
As long as food is available, Oscars will eat. At some point they cannot fit any more food into their bellies... but they keep cramming it into their mouths. At that point it becomes your responsibility to find that limit when they are filled (as Oscars are never full, but can be filled) and then stop adding more food.
If you are concerned that he is eating the food but little or none is making it into his belly, I highly doubt that would be the case. If your Oscar was ill to the point he wasn't ingesting food, he would lose his appetite and wouldn't eat.
My Oscars eat like pigs and blow food out of their mouths and gills all the time. Usually a sign I over fed them. Sometimes they keep eating just to pick on the other fish who seem to linger beneath the Oscars waiting for them to finish so everyone else can eat. (the Oscars rule my tank).
