This is a very stupid sentence. Koreans do not say like this way.
BUis2, So how should the question be asked in your enlighened opinion? How would an intelligent adult Korean phrase the question in various scenarios?
Can you also say "우리의 피자가 언제 먹혔어요?"
It is grammatically correct, but Koreans usually don't say it using passive verb. If you want to say this sentence, "우리가 언제 피자를 먹었어요?"(=When did we eat our pizza?) is more natural.
What if we did not know someone else or a dog ate our pizza, and we came into the room and were surprised to see the empty box? haha
Why not 먹혔다?