Can anyone help me identify this dish? It was originally at a Chinese restaurant in my hometown.

I tried posting this in r/chinesefood, but someone told me to try posting it here. I can’t figure out what this dish called so that I may cook it. The restaurant it’s from was based in rural Eastern Tennessee.

The Chinese restaurant referred to it as “Japanese Chicken”. The dish has a sweet and savory taste. The chicken is seared or grilled until there's black slightly crispy sections on it. There is no breading of any sort. It's mixed with onions and black pepper from what I remember. It has a dark brown sort of sauce to it. The sauce and chicken both have a fatty flavor and consistency, it’s definitely made of chicken thighs.

Never had anything like it at any other restaurant but the one from my hometown. But sadly I’ve moved away years ago and can’t get this anymore. So I want to make it myself. Any ideas would help me a lot!