Gusto is offering potatoes topped with mentaiko (spicy cod eggs) and mayonnaise. Mentaiko and mayonnaise on potatoes is a very common item in Japan. One reason I mention it here is in contrast to yesterday when I mentioned the use of Hokkaido potatoes in a different Gusto side dish. Here at the same restaurant, they are advertising Idaho potatoes. Japanese restaurants and customers pay attention to where ingredients are sourced, and it is often prominent on the menu.
Photo is a web capture for explanatory purposes, copyright belongs to the company.