Add the onions to a microwave-safe bowl, cover it with lid or plastic wrap, and microwave at 600 watts for about four minutes twenty seconds. The goal is to get them soft and just starting to brown. Let these cool off a bit.
Add the ground beef, cream cheese, panko, egg, Worcestershire sauce, soy sauce, and cooled onions to a bowl and use your hands to knead the mixture together until it's uniform in color.
Shape the mixture into 6-8 patties. Smack the patties between your hands to force out any air and seal up any cracks.
Put a spoonful of potato starch into a fine-mesh sieve and dust both sides of the patties with a thin, even coating. You can pat them between your hands again to remove any excess starch.
Heat a frying pan over medium heat and add a splash of oil. Add as many patties as you can get into the pan without overcrowding it.
Fry the Hamburg Steaks until they're cooked about 1/4 of the way through and flip them over. Turn down the heat to medium-low and brown the second side.
Flip the patties periodically to evenly brown both sides, and the internal temperature reads 140F (60C) on an instant-read thermometer.
Transfer the Hamburger Steaks onto a plate. If your pan didn't fit all the patties, fry the remaining patties now.
Once all of the patties have been cooked, turn off the heat and use paper towels to wipe out all of the pan's grease and particulate matter.
Add the ingredients for the teriyaki sauce to the clean pan and turn the stove on to high heat. Boil the sauce until it starts to thicken.
Return the Hamburg patties to the pan and roll them around in the sauce until they are coated in a thick, shiny layer of sauce, and the glaze has started to caramelize.