"They serve fish and potatoes."
Translation:Riarann siad iasc agus prátaí.
Riar is a transitive verb where the object is the thing being "served up".
Freastail is a transitive verb where the object is the thing or person that service is being given to - freastalaíonn siad ar an bpobal - "they serve the public".
In English you need context to tell whether "They served Bacon" is a statement about breakfast, or about the people who work for the actor, Kevin Bacon. In irish, you use two different verbs.
Do Irish people literally ask for "fish and potatoes" when they ask for fish and chips in Irish in Ireland?