Japan's Mos Burger chain is now serving a 'Nure Burger' with a crazy burger bun that's drenched in sauce before serving. This takes inspiration from a popular street food from Turkey, the islak burger, which is better identified simply as a "wet burger."
A Napolitan sauce is used to coat the entire outside of the Nure Burger, formed from a blend of thick tomato sauce, ketchup, Worcestershire sauce, plus grated onion and garlic.
Part of the reason people gravitate towards hamburgers is that the buns neatly contain all the contents of the burger and keep their hands free from messes. However, the rise of crazy burger buns made from spaghetti noodles, tomatoes and sticky donut halves shows that many consumers want food that is novel inside and out, even if it means it will be inconvenient or extremely messy to eat.