、。
I'm starving.
Literal
I [topic-、] belly-hungry is [explanatory-んだ].
腹ペコ is a compound: 腹 ('belly') + ペコ (from ぺこぺこ, an onomatopoeia for 'empty/hollow'). Casual and very common expression for being hungry — more vivid than お腹が空いた. 腹 is a more casual/masculine word for 'belly' than お腹. んだ provides emphatic explanation.