Is there a shorter alternative for "Enjoy your meal"?
Unfortunately, no. However, the French phrase bon appetit is very widely known, and you can use that as an alternative.
A very informal option would be to say Dig in!, though this has the connotation of eating sloppily or in large amounts, and doesn't necessarily carry the idea of enjoying an elegant, modestly portioned meal.
It is common in US restaurants for serving staff to say, "Enjoy!" upon placement of the meal.
It is also widely disliked and thought to be overly breezy.