"Avez-vous fini votre petit-déjeuner ?"

Translation: Are you through with your breakfast?

[eunoia]

Could you also translate this as "Did you finish your breakfast?"?

[bucko]

I think "Have you finished your breakfast?" is a slightly more precise translation than "did you".

[lkt005]

"Did you finish" would be "est-ce que tu as fini..." or "est-ce que vous avez fini..."