Best pizza/things to do near Napoli Centrale Station?

Hello!

My gf and I will be in Rome, Florence and Venice between xmas and early Jan. We're planning to visit Pompeii from Rome as a day trip, taking the train both ways. We have a Pompeii tour booked for 10:30am. We're expecting to be finished at Pompeii around 2-3pm (let me know if we should budget more time!) and we're looking at a ~8pm return train to Rome.

My question: how would you spend ~5h near Napoli Centrale? Recognizing we won't get to see much of the city, we're just looking for a place to walk around and take in the city for a bit before grabbing some dinner (ideally pizza) before our return train. We'll be there on a Sunday, if that matters.

Thanks in advance!