Stomach acid can produce what seems like hunger. Whenever I stop my PPI, I have that symptom of apparent hunger after I eat, it lasts for a few days then I'm back to normal. If I remember what I saw in a journal article, maximum acid production is around 45 minutes after eating.
If you stopped your PPI, or decreased it, after surgery, that could be it. Or maybe your stomach is irritated from the surgery in general, and is hypersensitive to acid production, causing what seems like hunger.