You mean foods that are strictly “American” in origin?
How about any restaurant which serves potatoes, corn, peppers, tomatoes, chocolate, peanuts, clams, cranberries, cassava, avocadoes, papayas, pecans, hickories, blueberries, chokecherries, currents, elderberries, turkey, …?
All are “ethic American” in origin.
With all due respect to KFC and Popeye’s, whose products I have enjoyed, authentic southern fried chicken bears little resemblance to fast food fried chicken. You need to travel down south and eat at non-franchised hole in the wall restaurants where cast iron chicken fryers are passed down from generation to generation. I doubt KFC or Popeye’s soak their chicken pieces in buttermilk overnight, or take care to use fresh peanut oil or lard to fry their chicken. That’s what I think of when I think about ethnic American cuisine. I hope that’s what the OP was thinking about when he posted his question.
You can get a great hamburger in Peru at Bembos.