Hello.
Interesting question but the answers will be as varied as the answers to, "what makes a happy couple?"
The process will vary from an eat-in Kebab, McDonalds, KFC, etc to the smart causal chains - Wagamama, Pizza Express, Zizzi Zizzi to a Michelin star restaurant in Mayfair.
Up to the high end, most dishes will be prepped and the 'Chefs' - read Cooks - will be finishing them off. This keeps costs low, maintains consistency and reduces the chance of food poisoning.
Most trained Chef's are expensive, commercially inept, don't like being told what to do and have massive ego's. They are a distraction most of the chains can easily do without.
Personally, I'd be more concerned about hygiene and cleanliness standards behind the scenes. Food is generally of a high standard in the UK regardless of where you eat it. Ambiance, service and people watching count for a lot for me.
Best wishes to all.
Zack 😚@IgnoreTheNonsense