A la fin du repas votre serveur vous demande “Ça a été?”
You’ve finished your main dish (le plat) and as your waiter is taking away the dishes, he or she asks “”Ça a été?” My ear always hears it as “Ça était…?” as if he is asking me to fill in the blank for an experience of unlimited duration. But of course, he or she is using the passé composé since the action, “Ça” (short for cela) started and has now completed.
So how do you answer this question now that you know what they are getting at? If the food was good, use any number of adjectives to describe your reaction: “délicieux,” “formidable,” “un délice, “excellent.” You are free to use the simple “tres bon” though you get no extra stars for vocabulary.