In Japanese there are two words that sound a bit like "hamburger". One, "hanbaagaa" (ハンバーガー）, means hamburger as in something you might find at McDonald's. Ground meat and bread being the significant points. The other word, "hanbaagu" (ハンバーグ), means ground meat patty but no bread. Usually served with rice, some sauce (there may be many choices if in a restaurant) or カレー (karee, Japanese curry).
I am told "hanbaagaa" is what Japanese people think "hamburger" sounds like and "hanbaagu" comes from "hamburg steak" with the steak part removed to shorten the expression.
The photo is my hanbaagu from our 3 A.M. meal at "Bikkuri Donki"when we closed early on Monday morning in the Magic Bar. Bikkuri Donki means "Surprised Donkey". As far as I know, the surprised part reflects the impact this chain of hambaagu restaurants has on the customers and the donkey part comes from comparing themselves to McDonald's. McDonald's is then a thorough bread (fast!) horse, while the donkey is slow paced, meaning you can take your time and relax at your own pace at Bikkuri Donki.