"Ole hyvä, yksi tomaatti" is not accepted. I've experienced this with several sentences that include "Here you are". Also, I think "Here you go" should be accepted, too.
It said in the tips section for one of the lessons that "ole hyvä" generally goes at the end of the phrase. So you would only say "yksi tomaatti, ole hyvä", and never "ole hyvä, yksi tomaatti."
As a native speaker, I would say both are ok, even if generally you would use ole hyvä at the end.
But in English, it works either way, and only one is accepted.
In spoken Finnish, people might say that - coming directly from my Finnish spouse.