Hybrid of two phrases: 1) "nom nom nom," which is an onomatpoeia for the act of eating and
2) "going to town," which is used in an adverbial sense to describe the vigor with which an action is taken, e.g., "going to town on that burrito" meaning to scarf it down quickly.
god, i haven't eaten all morning. i'm 'bout to go to nom nom town on that steak and eggs.