I'm curious if you could clarify what edifice you're interested in visiting.
The Primatiale Saint-Jean de Lyon is commonly referred to as Cathédral Saint-Jean. It's where Lyon's archdiocese is located. It has a complex and interesting astronomical clock, if you find that sort of thing of interest.
However, most tourists seem more focused on seeing the somewhat more gaudy Basilique de Notre-Dame de Fourvière, up the hill from Vieux Lyon and near the Roman ampitheatres.
To which are you referring when you mention "the cathedral?"
As for food, there are several places to get food in Gare Part-Dieu, but the range of options is somewhat limited. However, directly across the street from the train station (west side: Boulevard Marius Vivier Merle) is one of the largest shopping centers in France with dozens of restaurants serving many types of food from many cultures.