Why-y

One thing that's puzzled me for a while, is why do Japanese Americans add an extra vowel at the end of some words. For example, "I bought some sushi-i." It's sushi. But somehow there's an extra "i". It sounds like "su-Shii" as if it's two words with a heavy accent on the second half of the word.

Another one I've heard is gyoza. It's gyoza. That's it. But I've heard it as "gyo-za-a" with three syllables.

I know there's more!