Imma disagree, given that barbacoa was actually a type of building, used by the Taino Indians... who lived in Puerto Rico hence part of America.
For foods invented after the US became a country, I'll note there're a few:
Corn Dogs were invented in 1942 by Nate Fletcher, a Texas Carnival entrepreneur who wanted his hot dogs to be easier to carry at the carnival.
Cobb Salad was invented by Brown Derby owner Bob Cobb in 1937.
Salt Water Taffy was invented in Atlantic City by store owner David Bradley in 1883.
S'mores were invented by the Girl Scouts in 1927.
The Graham Crackers S'mores are made from were invented by Presbyterian minister Sylvester Graham (Father of Vegetarianism) in 1838, who believed that eating the crackers would cause teenagers to not think about sex. It didn't work but the Graham diet was a brief fad among people who didn't understand teenagers.