You have to train yourself to eat more, not only at each sitting, but throughout the day.
Start by eating or downing a huge shake immediately when you wake up, that will kicstart your hunger for lunch etc.
Before you know it you will be painfully hungry between meals on 4,000 cals a day like me.
Could also inject a peptide called GHRP-6 it is notorious for making you ravenously hungry.