A lot depends on customer complaints. The the people who copied the restaurant's ID and menu serve good food, the harmed person is the original. This is a lot like me making fake Coca-Cola - as long as I deliver a good tasting clean product I could get away with this for ages. Now this restaurans is aware, they could speak with the police or FBI(if it crosses state lines?). If the police do not find a cause to proceed, he can sue them for "passing off" https://en.wikipedia.org/wiki/Passing_off

This might work based on a letter. Best way to go is make an order and get it delivered to you and ask the delivery person (of course, video and plate number etc) and ask him where he picked up the food - if he wiggles, tell them you have his plate and video and you will call the IRS about his undeclared income and the state about undeducted salaries - hopefully this will pursuade him to speak up. If not, it gets harder as you will have to track them to their lair. You may get by with a cease and desist letter that you find online and adapt to your case and mail to them at their lair? This is an easy form of copying for one of these 'container kitchens' that a lot of restaurants already use to deal with voilume online orders. https://www.google.com/search?q=container+kitchens&oq=contai...

Anyone who owns one of these can easily add other foods from other places - even unwilllingly.