Verbs are declined differently for the female zij and the plural zij.
- Zij eten pasta = They eat pasta
- Zij eet pasta = She eats pasta
- Zij zijn groot = They are big
- Zij is groot = She is big
I know that you have to watch for the conjugation of the verb to make distinction between the two "zijn", but in this "listen and write what you hear" example it sounds "Zij eet een pasta" and it also sounds "Zij eten pasta" - I could not decide which one I herd.
You're right that those sound the same, this can also be the case with human speakers since the pause before een can practically disappear. In this case it would normally be zij eten because een pasta is rarely used compared to pasta without the article. But there are cases where you won't know: Zij eet een vis vs Zij eten vis, then it's all about context.