Hambagu (ハンバーグ) is a Japanese hamburger steak served in western style Japanese restaurants. It is sometimes also called a Hamburg steak. Thicker than a regular steak, it is usually served with a thick sauce made using a mixture of ketchup and tonkatsu sauce. It is usually served with rice instead of bread buns like a Western style hamburger.
The meat is usually a mixture of beef and pork, with added flavour from sauteed onions. I used these recipes here and here as reference when I made the hambagu at home, but to be honest I just tossed a couple tablespoons of panko with a bit of beaten egg and mixed with ground beef and sauteed onions. (This only made one hamburger steak, as it was for Z1 who was home sick from school).
Shape into a thick beef patty and fry it as you would usually do with a meat patty.
For the sauce, I would have mixed equal quantities of tonkatsu sauce with ketchup and heated it before pouring over the hamburger steak. Lucky for me (or if you would call it lazy) I found a bottle of pre-mixed sauce in the Japanese supermarket and used that instead. It is from the Bulldog brand.
Here is my hambagu bento, served with a bear onigiri and a little cheese bear over the hamburger steak.