Rashi specifically defines shiboles shual as oats (avino b’laz). The problem with that is as described above by other posters.
1. oats does not look like the other four
2. oats are a not from genus triticum as are the other four.
3. oats have no (or little) gluten.
4. Oats did not grow in Eretz Yisroel or Bavel.
Personally, I think that the description given of shiblos shual fits emmer wheat (a different species from bread wheat)which grew in abundance in Israel and Bavel. One might say that Rashi, not being familiar with other varieties of wheat, was simply mistaken, but I think that you have to be a Reshone to say that. Personally, I do not and would not use oat matzoh for matzas mitzvah nor do I make hamotzi on oat products.